SEC Info℠

Home

Search

My Interests

Help

Sign In

Please Sign In

Atmi Inc – ‘DEFM14A’ on 3/11/14

On:  Tuesday, 3/11/14, at 8:30pm ET   ·   As of:  3/12/14   ·   Effective:  3/12/14   ·   Accession #:  1193125-14-94262   ·   File #:  1-16239

in

this entire Filing. an “Entity” Search.

Show

Documents searched

and

each “hit”. the 1st “hit”.

↓↑Hints

 Text Wildcards:  ? (any letter/digit),  * (many).  Search Logic:  for Documents:  & (and),  | (or);  for Text:  | (anywhere),  "(&)" (near).  Details... 

  As Of                Filer                Filing    For·On·As Docs:Size              Issuer               Agent

 3/12/14  Atmi Inc                          DEFM14A     3/12/14    1:1.3M                                   Donnelley … Solutions/FA

Document/Exhibit                   Description                      Pages   Size 

 1: DEFM14A     Definitive Proxy Solicitation Material - Merger or  HTML   1.18M 
                          Acquisition                                            

Table of Contents

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant  x                             Filed by a party other than the Registrant  ¨

Check the appropriate box:

ATMI, INC.

(Name of Registrant as Specified In Its Charter)

N/A

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

Table of Contents

ATMI, INC.

7 COMMERCE DRIVE

DANBURY, CONNECTICUT 06810

(203) 794-1100

March 11, 2014

Dear Stockholder:

We cordially invite you to attend the special meeting of stockholders of ATMI, Inc. (“ATMI”), which will be held at ATMI’s corporate offices located at 7 Commerce Drive, Danbury, Connecticut 06810 at 10:00 a.m. EDT on April 15, 2014.

At the special meeting, you will be asked to consider and vote upon:

1. a proposal to adopt the Agreement and Plan of Merger, dated as of February 4, 2014 (as it may be amended from time to time), by and among ATMI, Entegris, Inc. (“Entegris”) and Atomic Merger Corporation, a wholly owned subsidiary of Entegris (“Merger Sub”);

2. a proposal to adjourn the special meeting, if necessary, to solicit additional proxies if there are insufficient votes at the time of the special meeting to adopt the merger agreement; and

3. a non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger.

If the merger is completed, you will be entitled to receive $34.00 in cash, without interest and less any applicable withholding taxes, for each share of ATMI common stock you own as of the date of the merger.

After careful consideration, our board of directors, by unanimous vote, approved and declared advisable the execution, delivery and performance of the merger agreement and the transactions contemplated by the merger agreement, including the merger, and determined that entering into the merger agreement and consummating the merger, are fair to, and in the best interests of, ATMI’s stockholders. Accordingly, our board of directors recommends that you vote “FOR” the proposal to adopt the merger agreement, “FOR” the proposal to adjourn the special meeting, if necessary, and “FOR” the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger.

The proxy statement accompanying this letter provides you with detailed information about the proposed merger and the special meeting of stockholders to vote on the adoption of the merger agreement. We encourage you to read the entire proxy statement and the merger agreement carefully. A copy of the merger agreement is attached as Annex A to the accompanying proxy statement. You may also obtain more information about ATMI from documents we have filed with the Securities and Exchange Commission.

Your vote is very important, regardless of the number of shares of stock that you own. The merger cannot be completed unless the merger agreement is adopted by the affirmative vote (in person or by proxy) of the holders of at least a majority of the outstanding shares of ATMI common stock entitled to vote at the special meeting. If you fail to vote on the proposal to adopt the merger agreement, the effect will be the same as a vote “AGAINST” the adoption of the merger agreement.

Table of Contents

IT IS IMPORTANT THAT YOUR SHARES BE REPRESENTED, EVEN IF YOU DO NOT PLAN ON ATTENDING THE SPECIAL MEETING IN PERSON. ACCORDINGLY, WE URGE YOU TO VOTE BY COMPLETING, SIGNING, DATING AND PROMPTLY RETURNING THE ENCLOSED PROXY CARD IN THE ENVELOPE PROVIDED, OR YOU MAY VOTE THROUGH THE INTERNET OR BY TELEPHONE AS DIRECTED ON THE ENCLOSED PROXY CARD. IF YOU RECEIVE MORE THAN ONE PROXY CARD BECAUSE YOU OWN SHARES THAT ARE REGISTERED DIFFERENTLY, PLEASE VOTE ALL OF YOUR SHARES SHOWN ON ALL OF YOUR PROXY CARDS.

On behalf of your board of directors, thank you for your continued support.

Sincerely,

Douglas A. Neugold

Chairman of the Board, President and

Chief Executive Officer

Table of Contents

ATMI, INC.

7 COMMERCE DRIVE

DANBURY, CONNECTICUT 06810

(203) 794-1100

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

TO BE HELD ON APRIL 15, 2014

To Stockholders of ATMI, Inc.:

Notice is hereby given that a special meeting of stockholders of ATMI, Inc., a Delaware corporation (“ATMI”), will be held at ATMI’s corporate offices located at 7 Commerce Drive, Danbury, Connecticut 06810 at 10:00 a.m. EDT on April 15, 2014, for the following purposes:

1. to consider and vote upon a proposal to adopt the Agreement and Plan of Merger, dated as of February 4, 2014 (as it may be amended from time to time), by and among ATMI, Entegris, Inc., a Delaware corporation (“Entegris”) and Atomic Merger Corporation, a Delaware corporation and a wholly owned subsidiary of Entegris (“Merger Sub”);

2. to consider and vote upon a proposal to adjourn the special meeting, if necessary, to solicit additional proxies if there are insufficient votes at the time of the special meeting to adopt the merger agreement; and

3. to consider and vote upon a non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger.

After careful consideration, our board of directors, by unanimous vote, has approved and declared advisable the execution, delivery and performance of the merger agreement and the transactions contemplated by the merger agreement, including the merger, and has determined that entering into the merger agreement and consummating the merger, are fair to, and in the best interests of, the Company’s stockholders.

OUR BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT YOU VOTE “FOR” THE ADOPTION OF THE MERGER AGREEMENT, “FOR” THE PROPOSAL TO ADJOURN THE SPECIAL MEETING, IF NECESSARY, AND “FOR” THE NON-BINDING ADVISORY PROPOSAL TO APPROVE THE GOLDEN PARACHUTE COMPENSATION PAYABLE TO ATMI’S NAMED EXECUTIVE OFFICERS IN CONNECTION WITH THE MERGER.

Only stockholders of record of ATMI common stock at the close of business on March 10, 2014, the record date for the special meeting, are entitled to notice of and to vote at the special meeting and at any adjournment or postponement of the special meeting. A list of stockholders entitled to vote at the special meeting will be available for inspection by stockholders of record during business hours at ATMI’s corporate offices located at 7 Commerce Drive, Danbury, Connecticut 06810 for ten days prior to the date of the special meeting and will also be available at the special meeting.

Your vote is very important, regardless of the number of shares of stock that you own. The adoption of the merger agreement requires the affirmative vote (in person or by proxy) of the holders of at least a majority of the outstanding shares of ATMI common stock entitled to vote at the special meeting. Each of the proposal to adjourn the special meeting, if necessary, to solicit additional proxies and the non-binding advisory proposal to

Table of Contents

approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger requires the affirmative vote (in person or by proxy) of the holders of at least a majority of the voting power present and entitled to vote at the special meeting.

Whether or not you plan to attend the special meeting, we urge you to vote your shares by completing, signing, dating and returning the accompanying proxy card as promptly as possible in the postage-paid envelope or to submit your proxy by telephone or the Internet prior to the special meeting to ensure that your shares will be represented at the special meeting. If you sign and return your proxy card without indicating how you wish to vote, your proxy will be voted “FOR” the adoption of the merger agreement and “FOR” the proposal to adjourn the special meeting, if necessary, to solicit additional proxies if there are insufficient votes to adopt the merger agreement at the time of the special meeting and “FOR” the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger. If you fail to return your proxy card or fail to submit your proxy by telephone or the Internet and do not vote in person at the special meeting, it will have the same effect as a vote “AGAINST” the adoption of the merger agreement, but will not affect the outcome of the vote regarding the proposal to adjourn the special meeting, if necessary, to solicit additional proxies or the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger. Any stockholder attending the special meeting may vote in person even if he or she has already voted by proxy card, telephone or Internet; such vote by ballot will revoke any proxy previously submitted. If you hold your shares through a bank, broker or other custodian, you must provide a legal proxy issued from such bank, broker or other custodian in order to vote your shares in person at the special meeting.

The Company’s stockholders who do not vote in favor of the adoption of the merger agreement will have the right to seek appraisal of the fair value of their shares of ATMI common stock if the merger contemplated by the merger agreement is completed, but only if they submit a written demand for appraisal of their shares before the taking of the vote on the merger agreement at the special meeting and they comply with all requirements of Delaware law, which are summarized in greater detail in the accompanying proxy statement.

The accompanying proxy statement is dated March 11, 2014 and is first being mailed to stockholders of the Company on or about March 12, 2014.

By Order of the Board of Directors,

Patrick J. Shima

Secretary

March 11, 2014

Danbury, Connecticut

PLEASE DO NOT SEND YOUR STOCK CERTIFICATES AT THIS TIME. IF THE MERGER IS COMPLETED, YOU WILL BE SENT INSTRUCTIONS REGARDING THE SURRENDER OF YOUR STOCK CERTIFICATES.

Table of Contents

TABLE OF CONTENTS

Table of Contents

Table of Contents

1

Table of Contents

2

Table of Contents

3

Table of Contents

4

Table of Contents

5

Table of Contents

6

Table of Contents

7

Table of Contents

8

Table of Contents

9

Table of Contents

10

Table of Contents

QUESTIONS AND ANSWERS ABOUT THE SPECIAL MEETING AND THE MERGER

The following questions and answers are intended to briefly address some commonly asked questions you may have regarding the special meeting, the merger agreement and the proposed merger. These questions and answers may not address all questions that may be important to you as a stockholder of the Company. Please refer to the more detailed information contained elsewhere in this proxy statement, the annexes to this proxy statement and the documents referred to or incorporated by reference in this proxy statement, which you should read carefully. See the section of this proxy statement entitled “Where You Can Find More Information.”

11

Table of Contents

12

Table of Contents

13

Table of Contents

14

Table of Contents

15

Table of Contents

16

Table of Contents

Call Collect: (212) 929-5500

Toll Free: (800) 322-2885

Email to: proxy@mackenziepartners.com

Address: 105 Madison Avenue, New York, New York 10016

17

Table of Contents

CAUTIONARY STATEMENT CONCERNING FORWARD-LOOKING INFORMATION

This proxy statement, and the documents to which we refer you in this proxy statement, contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Exchange Act. Forward-looking statements include, among others, information concerning the possible or assumed future results of operations of the Company, the expected completion and timing of the merger and other information relating to the merger. There are forward-looking statements throughout this proxy statement, including, without limitation, under the headings “Proxy Statement Summary,” “Questions and Answers about the Special Meeting and the Merger,” “Proposal 1: Adoption of the Merger Agreement,” “Proposal 1: Adoption of the Merger Agreement — Certain Financial Forecasts,” “Proposal 1: Adoption of the Merger Agreement — Governmental and Regulatory Approvals” and “Proposal 1: Adoption of the Merger Agreement — Opinion of ATMI’s Financial Advisor.” Forward-looking statements can be identified by words such as “believes,” “expects,” “predicts,” “estimates,” “anticipates,” “continues,” “contemplates,” “projects,” “intends,” “may,” “will,” “could,” “should” or “would” or similar expressions, or by discussion of competitive strengths or strategy that involve risks and uncertainties. These statements, which are based on information currently available to us, are not guarantees of future performance, actual outcomes or developments and may involve risks and uncertainties that could cause our actual outcomes, developments, growth, results of operations, performance and business prospects and opportunities to materially differ from those expressed in, or implied by, these statements. In addition to other factors and matters contained or incorporated in this document, these statements are subject to risks, uncertainties, and other factors, including, among others:

The forward-looking statements contained in this proxy statement speak only as of the date on which such statements were made and we undertake no obligation, other than as may be required under the federal securities laws, to publicly update or revise any forward-looking statements, whether as a result of new information, future

18

Table of Contents

events or otherwise. We do not assume responsibility for the accuracy and completeness of forward-looking statements. Any or all of the forward-looking statements contained in this proxy statement and in any other public statements that are made may prove to be incorrect. This may occur as a result of inaccurate assumptions or as a consequence of known or unknown risks and uncertainties. All of the forward-looking statements are qualified in their entirety by reference to the risk factors discussed above and under the caption “Risk Factors” of our most recent filings on Forms 10-Q and 10-K and on our Form 8-K filed on February 4, 2014. We operate in a continually changing business environment, and new risk factors emerge from time to time. We cannot predict these new risk factors, nor can we assess the impact, if any, of the new risk factors on our business or the extent to which any factor or combination of factors may cause actual results or outcomes to differ materially from those expressed or implied by any forward-looking statement. In light of these risks, uncertainties and assumptions, the forward-looking events discussed in this proxy statement might not occur.

19

Table of Contents

THE PARTIES TO THE MERGER

ATMI, Inc.

7 Commerce Drive

Danbury, CT 06810

(203) 794-1100

ATMI (NASDAQ-GS: ATMI), a Delaware corporation, is among the leading suppliers of high performance materials, materials packaging and materials delivery systems used worldwide in the manufacture of microelectronics devices. ATMI’s products consist of “front-end” semiconductor performance materials, sub-atmospheric pressure gas delivery systems for safe handling and delivery of toxic and hazardous gases to semiconductor process equipment, and high-purity materials packaging and dispensing systems that allow for the reliable introduction of low volatility liquids and solids to microelectronics processes. ATMI targets semiconductor and flat-panel display manufacturers, whose products form the foundation of microelectronics technology rapidly proliferating through the consumer products, information technology, automotive, and communications industries.

For more information about us, please visit our website http://www.atmi.com. Our website address is provided as an inactive textual reference only. The information provided on our website is not part of this proxy statement, and therefore is not incorporated by reference. See also the section of this proxy statement entitled “Where You Can Find More Information.” ATMI common stock is publicly traded on the NASDAQ Global Select Market under the trading symbol “ATMI”.

Entegris, Inc.

129 Concord Road

Billerica, MA 01821

(978) 436-6500

Entegris (NASDAQ-GS: ENTG), a Delaware corporation, is a leading provider of a wide range of products and services for purifying, protecting and transporting critical materials used in processing and manufacturing in the microelectronics and other high-technology industries. Entegris derives most of its revenue from the sale of products and services to the semiconductor and related industries. Entegris’s customers consist primarily of semiconductor manufacturers, semiconductor equipment and materials suppliers as well as thin film transistor-liquid crystal display and hard disk manufacturers, which are served through direct sales efforts, as well as sales and distribution relationships, in the United States, Asia, Europe and the Middle East.

Atomic Merger Corporation

c/o Entegris, Inc.

129 Concord Road

Billerica, MA 01821

(978) 436-6500

Atomic Merger Corporation is a Delaware corporation and a wholly owned subsidiary of Entegris. It was formed solely for the purpose of effecting the merger and the transactions contemplated by the merger agreement, and it has not engaged in any other business.

20

Table of Contents

THE SPECIAL MEETING

Date, Time, Place and Purpose of the Special Meeting

This proxy statement is being furnished to our stockholders as part of the solicitation of proxies by our board of directors for use at the special meeting to be held at ATMI’s corporate offices located at 7 Commerce Drive, Danbury, Connecticut 06810 at 10:00 a.m. EDT on April 15, 2014, or at any postponement or adjournment thereof. The purpose of the special meeting is for our stockholders to consider and vote upon a proposal to adopt the merger agreement (and to approve (i) the adjournment of the special meeting, if necessary, to solicit additional proxies if there are insufficient votes at the time of the special meeting to adopt the merger agreement; and (ii) a non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger). Stockholders holding a majority of the issued and outstanding shares of ATMI common stock at the close of business on the record date must vote to adopt the merger agreement in order for the merger to occur. A copy of the merger agreement is attached as Annex A to this proxy statement.

Board of Directors Recommendation

After careful consideration, our board of directors, by unanimous vote, approved and declared advisable the execution, delivery and performance of the merger agreement and the transactions contemplated by the merger agreement, including the merger, and determined that entering into the merger agreement and consummating the merger, are fair to, and in the best interests of, ATMI’s stockholders. Our board of directors recommends that you vote “FOR” the proposal to adopt the merger agreement, “FOR” the proposal to adjourn the special meeting, if necessary, to solicit additional proxies and “FOR” the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger. For a discussion of the material factors considered by our board of directors in reaching its conclusions, see the section of this proxy statement entitled “Proposal 1: Adoption of the Merger Agreement — Reasons for the Merger; Recommendation of Our Board of Directors.”

Record Date and Quorum

We have fixed the close of business on March 10, 2014 as the record date for the special meeting, and only holders of record of shares of ATMI common stock on the record date are entitled to vote at the special meeting. As of the close of business on the record date for the special meeting, there were 33,148,248 shares of ATMI common stock entitled to be voted at the special meeting. Each share of ATMI common stock outstanding on the record date entitles its holder to one vote on all matters properly coming before the special meeting.

The presence at the special meeting in person or by proxy of the holders of a majority of the issued and outstanding shares of our capital stock entitled to vote at the special meeting as of the close of business on the record date will constitute a quorum for purposes of considering the proposals at the special meeting. Shares of ATMI common stock represented at the special meeting but not voted, including shares of ATMI common stock for which we have received proxies indicating that the submitting stockholders have abstained and broker non-votes will be treated as present at the special meeting for purposes of determining the presence or absence of a quorum for the transaction of all business. A broker non-vote occurs on an item when a broker is not permitted to vote on that item without instructions from the beneficial owner of the shares, and no instructions are given.

Vote Required for Approval

The adoption of the merger agreement requires the affirmative vote (in person or by proxy) of the holders of a majority of the outstanding shares of ATMI common stock at the close of business on the record date. For the proposal to adopt the merger agreement, you may vote “FOR,” “AGAINST” or “ABSTAIN.” Abstentions will not be counted as votes cast or shares voting on the proposal to adopt the merger agreement, but will count for the purpose of determining whether a quorum is present. If you abstain, it will have the same effect as a vote “AGAINST” the adoption of the merger agreement.

21

Table of Contents

Brokers, banks or other nominees who hold shares of ATMI common stock in “street name” for customers who are the beneficial owners of such shares may not give a proxy to vote those customers’ shares in the absence of specific instructions from those customers. These non-voted shares of ATMI common stock will not be counted as votes cast or shares voting and will have the same effect as votes “AGAINST” approval and adoption of the merger agreement.

Approval of each of (i) any proposal to adjourn the special meeting, if necessary, for the purpose of soliciting additional proxies and (ii) the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger requires the affirmative vote of a majority of the shares of ATMI common stock present in person or represented by proxy at the special meeting and entitled to vote on the matter. A failure to vote your shares of ATMI common stock or a broker non-vote will have no effect on the outcome of any vote to adjourn the special meeting or to approve the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger. An abstention will have the same effect as voting “AGAINST” any proposal to adjourn the special meeting or to approve the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger.

As of March 10, 2014, the record date for the special meeting, our current directors and executive officers beneficially owned, and had the right to vote, in the aggregate, 1,644,200 shares of ATMI common stock, which represented approximately 4.84% of the outstanding shares of ATMI common stock. Our current directors and executive officers have informed us that they intend to vote all of their shares of ATMI common stock “FOR” the adoption of the merger agreement, “FOR” the adjournment of the special meeting, if necessary, to solicit additional proxies and “FOR” the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger.

Proxies and Revocation

In order for your shares of ATMI common stock to be included in the vote, if you are a stockholder of record, you must either have your shares voted by returning the enclosed proxy card or by authorizing your proxy or voting instructions by telephone or Internet or voting in person at the special meeting.

Record holders may vote or cause their shares of ATMI common stock to be voted by proxy using one of the following methods:

If no instructions are indicated on your signed proxy card, your shares will be voted “FOR” the adoption of the merger agreement, “FOR” adjournment of the special meeting, if necessary, to solicit additional proxies and “FOR” approval of the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger.

If your shares of ATMI common stock are held in “street name” by your broker, bank or other nominee, you should instruct your broker, bank or other nominee on how to vote your shares of ATMI common stock using the instructions provided by your broker, bank or other nominee.

WHETHER OR NOT YOU PLAN TO ATTEND THE SPECIAL MEETING, PLEASE COMPLETE, DATE, SIGN AND RETURN, AS PROMPTLY AS POSSIBLE, THE ENCLOSED PROXY CARD IN THE ACCOMPANYING REPLY ENVELOPE, OR SUBMIT YOUR PROXY BY TELEPHONE OR THE INTERNET. STOCKHOLDERS WHO ATTEND THE MEETING MAY REVOKE THEIR PROXIES AND VOTE IN PERSON.

22

Table of Contents

If you submit a proxy by telephone or the Internet or by returning a signed proxy card by mail, your shares will be voted at the special meeting as you indicate on your proxy card or by such other method. If you sign your proxy card without indicating your vote, your shares will be voted “FOR” the adoption of the merger agreement, “FOR” the adjournment of the special meeting, if necessary, to solicit additional proxies and “FOR” the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger.

If you abstain, your shares of ATMI common stock will be treated as present at the special meeting for purposes of determining the presence or absence of a quorum for the transaction of business; however, your shares will not be counted as votes cast or shares voting on the proposals. If you abstain, it will have the same effect as a vote “AGAINST” the proposals.

If your shares of ATMI common stock are held in “street name,” you will receive instructions from your broker, bank or other nominee that you must follow in order to have your shares voted. If you do not instruct your broker, bank or other nominee to vote your shares, it has the same effect as a vote “AGAINST” the proposal to adopt the merger agreement but will have no effect on the proposal to adjourn the special meeting, if necessary, to solicit additional proxies or the non-binding advisory proposal to approve the golden parachute compensation payable to ATMI’s named executive officers in connection with the merger.

Proxies received at any time before the special meeting, and not revoked or superseded before being voted, will be voted at the special meeting. If you hold your shares in your name as a stockholder of record, you have the right to change or revoke your proxy at any time before the vote taken at the special meeting by:

If you hold your shares through a broker, bank, or other nominee, you have the right to change or revoke your proxy at any time before the vote taken at the special meeting by following the directions received from your broker, bank or other nominee to change or revoke those instructions.

PLEASE DO NOT SEND IN YOUR STOCK CERTIFICATES WITH YOUR PROXY CARD. IF THE MERGER IS COMPLETED, A SEPARATE LETTER OF TRANSMITTAL WILL BE MAILED TO YOU THAT WILL ENABLE YOU TO RECEIVE THE MERGER CONSIDERATION IN EXCHANGE FOR YOUR ATMI STOCK CERTIFICATES.

Adjournments and Postponements

Although it is not currently expected, the special meeting may be adjourned or postponed for the purpose of soliciting additional proxies. Any adjournment may be made without notice, other than by an announcement made at the special meeting of the time, date and place of the adjourned meeting, provided that if the adjournment is for more than 30 days, or if after the adjournment a new record date is fixed for the adjourned meeting, notice of the adjourned meeting in accordance with the bylaws of the Company will be given to each stockholder of record entitled to notice of and to vote at the meeting. Holders of a majority of the shares of ATMI common stock present in person or represented by proxy at the special meeting and entitled to vote may adjourn or postpone the special meeting. Any signed proxies received by us in which no voting instructions are provided on the matter will be voted “FOR” an adjournment of the special meeting, if necessary, to solicit additional proxies. Any adjournment or postponement of the special meeting for the purpose of soliciting additional proxies will allow our stockholders who have already sent in their proxies to revoke them at any time prior to their use at the special meeting as adjourned or postponed.

23

Table of Contents

Rights of Stockholders Who Dissent From the Merger

Stockholders are entitled to statutory appraisal rights under Delaware law in connection with the merger. This means that you are entitled to have the value of your shares of ATMI common stock determined by the Delaware Court of Chancery and to receive payment based on that valuation. The ultimate amount you receive as a dissenting stockholder in an appraisal proceeding may be more than, the same as or less than the amount you would have received under the merger agreement.

To perfect your appraisal rights, you must submit a written demand for appraisal to us before the vote is taken on the merger agreement and you must not vote in favor of the adoption of the merger agreement. Your failure to follow exactly the procedures specified under Delaware law will result in the loss of your appraisal rights. See the section of this proxy statement entitled “Appraisal Rights” and the text of the Delaware appraisal rights statute, Section 262 of the DGCL, reproduced in its entirety as Annex C to this proxy statement. This proxy statement constitutes our notice to our stockholders of the availability of appraisal rights in connection with the merger in compliance with the requirements of Section 262 of the DGCL.

Solicitation of Proxies

This proxy solicitation is being made and paid for by us on behalf of our board of directors. In addition, we have engaged MacKenzie Partners, Inc. to assist in the solicitation of proxies for the special meeting, and we estimate that we will pay MacKenzie Partners, Inc. a fee of approximately $20,000. We also have agreed to reimburse MacKenzie Partners, Inc. for out-of-pocket expenses and to indemnify them against certain losses arising out of their proxy solicitation services. Our directors, officers and employees may also solicit proxies by personal interview, mail, e-mail, telephone, facsimile or other means of communication. These persons will not be paid additional compensation for their efforts. We will also request brokers, banks and other nominees to forward proxy solicitation material to the beneficial owners of shares of ATMI common stock that the brokers, banks and nominees hold of record. Upon request, we will reimburse them for their reasonable out-of-pocket expenses related to forwarding the material.

Questions and Additional Information

If you have more questions about the merger, need assistance in submitting your proxy or voting your shares, or need additional copies of the proxy statement or the enclosed proxy card, you should contact MacKenzie Partners, Inc., our proxy solicitor:

Call Collect: (212) 929-5500

Toll Free: (800) 322-2885

Email to: proxy@mackenziepartners.com

Address: 105 Madison Avenue, New York, New York 10016

24

Table of Contents

PROPOSAL 1

ADOPTION OF THE MERGER AGREEMENT

Background of the Merger

As part of its ongoing evaluation of business and strategic planning alternatives, ATMI’s board of directors, from time to time has discussed and reviewed strategic goals and alternatives. These reviews have included consideration of potential transactions and business combinations, as well as ATMI’s standalone business plans and prospects.

During the spring of 2013, representatives of ATMI’s management, prompted, in part, by concerns about the challenging market dynamics associated with the maturing microelectronics industry, prepared a preliminary analysis of various strategic alternatives potentially available to the Company, including maintaining the status quo, the return of cash to stockholders (through a dividend or share repurchase), taking ATMI private, one or more acquisitions and a sale of ATMI. At a meeting of the board of directors on May 22, 2013, representatives of ATMI’s management presented to, and discussed with, the board of directors this preliminary analysis. At the conclusion of the meeting, the board of directors decided that ATMI’s management and three directors, Mark Adley (ATMI’s lead independent director), Douglas Marsh and Mark Segall, would contact and begin interviewing investment banks to assist ATMI with its review of the potential strategic alternatives.

During June and July 2013, Messrs. Adley, Marsh and Segall, as well as members of ATMI’s management, met with representatives from four investment banks, including Barclays. The investment banks each made presentations regarding their capabilities and various strategic alternatives potentially available to ATMI. At the conclusion of the interviews, Messrs. Adley, Marsh and Segall and representatives of ATMI’s management determined that three of the investment banks, including Barclays, should make presentations to the entire board of directors at its next meeting.

On July 25, 2013, at a meeting of the board of directors, the board of directors received presentations from representatives of the three investment banks regarding various strategic alternatives potentially available to ATMI to maximize stockholder value and the advantages and disadvantages of each alternative. The alternatives included a sale of ATMI, one or more acquisitions for ATMI’s Microelectronics business and/or Life Sciences business and a spin-off or sale of ATMI’s Life Sciences business, as well as maintaining the status quo as a stand-alone company. In discussing a potential sale of ATMI, it was noted that due to the different focus between ATMI’s Microelectronics business and its Life Sciences business, the number of potential buyers for the entire Company was likely to be limited and, as a result, ATMI may need to explore separate sales of its Microelectronics business and its Life Sciences business in order to maximize stockholder value. The board of directors then discussed the presentations made by the three investment banks and determined, based on the input of the representatives of the investment banks at the meeting, to proceed with exploring a possible sale of ATMI because the board of directors considered this to be the option most likely to maximize stockholder value. The board of directors then authorized three directors, Messrs Adley, Marsh and Segall, to further evaluate the three investment banks and to recommend one of them to be ATMI’s financial advisor in connection with its evaluation of potential strategic alternatives.

On August 13, 2013, at a meeting of the board of directors, Mr. Adley updated the board of directors on discussions that he and Messrs. Marsh and Segall had with each of the three investment banks that had made presentations at the July 25th board meeting and that their recommendation was to select Barclays to advise ATMI in connection with its evaluation of potential strategic alternatives. The board of directors then approved the engagement of Barclays and authorized ATMI’s management to explore a sale of ATMI either in one transaction or in separate sales of its Microelectronics business and its Life Sciences business. Subsequently, ATMI entered into an engagement letter with Barclays, dated August 13, 2013, to act as financial advisor to ATMI.

25

Table of Contents

In the following weeks, representatives of ATMI’s management and representatives of Barclays discussed the structure and timing of a potential sale of ATMI, including separate sales of ATMI’s Microelectronics business and its Life Sciences business, while at the same time being opportunistic if a potential buyer for the entire company emerged. Other than Company A (as described below), no potential buyer in either the Microelectronics business sales process or the Life Sciences business sales process showed more than a preliminary interest in acquiring both the Microelectronics business and the Life Sciences business.

Beginning in early September 2013 and concluding on December 22, 2013 with the signing of a transaction with respect to the Life Sciences business, representatives of ATMI’s management, Barclays and ATMI’s legal counsel, Weil, Gotshal & Manges LLP (referred to in this proxy statement as Weil), on behalf of ATMI, conducted a sale process for ATMI’s Life Sciences business.

Beginning in late September 2013 through early October 2013, representatives of Barclays, on behalf of ATMI, contacted 21 potential strategic buyers for ATMI’s Microelectronics business, including Entegris, jointly identified by representatives of ATMI’s management and Barclays (including buyers that may have been interested in solely the Microelectronics business or both the Microelectronics business and the Life Sciences business). Representatives of ATMI’s management, after consultation with Barclays, determined not to contact any financial buyers because, among other reasons, the cash flow generated by the Microelectronics business likely would not be able to support the leverage that a financial buyer would need to put on the Microelectronics business to achieve its required return on investment. Barclays, on behalf of ATMI, subsequently distributed a form of a confidentiality agreement with certain standstill restrictions that would terminate upon the signing of a transaction for the sale of ATMI, together with certain initial information in the form of a summary memorandum, to the potential buyers. During this period, confidentiality agreements were negotiated and signed with nine potential buyers, including Entegris on September 25, 2013. The remaining potential buyers declined to move forward with the process for various reasons.

On September 25, 2013, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. At the meeting, representatives of Barclays provided an update to the board of directors on the processes for the potential sales of ATMI’s Microelectronics business and its Life Sciences business. With respect to the sale of ATMI’s Microelectronics business, representatives of ATMI’s management and Barclays updated the board of directors on the potential buyers that had been contacted and the timing for a signing of a potential transaction, which was expected to follow several weeks behind the signing for the sale of ATMI’s Life Sciences business (expected to be early December 2013) due to ATMI’s expectation that potential buyers of the Microelectronics business would need to understand the final structure of the Life Sciences business sale agreement to finalize bids for the Microelectronics business.

From October 1, 2013 through October 18, 2013, the nine potential buyers who executed confidentiality agreements, including Entegris, attended presentations regarding ATMI’s Microelectronics business conducted by representatives of ATMI’s management.

From October 11, 2013 through October 15, 2013, representatives of Barclays, on behalf of ATMI, sent a first round process letter for the sale of ATMI’s Microelectronics business to nine potential buyers who, based on conversations with representatives of Barclays, were interested in submitting an initial indication of interest and had signed a confidentiality agreement. The first round process letter indicated that initial indications of interests were due on October 24, 2013, and that bidders should submit initial indications of interests for ATMI’s Microelectronics business assuming that the Life Sciences business had already been sold and on an enterprise value (rather than per share) basis given uncertainties in the net after-tax cash proceeds from the sale of the Life Sciences business.

On October 16, 2013, the board of directors held a meeting at which representatives of ATMI’s management and Barclays were present. At the meeting, the representatives of Barclays provided an update to the board of directors on the processes for the potential sales of ATMI’s Microelectronics business and its Life Sciences business.

26

Table of Contents

On October 17, 2013, a potential buyer that we refer to as Company A, which executed a confidentiality agreement with ATMI, informed representatives of Barclays that it would not be moving forward with the Microelectronics business sales process as outlined in the first round process letter. On the same day, Company A submitted a letter to ATMI, which outlined a proposal for a strategic transaction between ATMI and Company A. The proposal provided for a stock-for-stock “merger of equals” type transaction in which Company A would acquire 100% of the outstanding shares of ATMI (including both the Microelectronics business and the Life Sciences business) in exchange for shares of common stock of Company A based on a fixed exchange ratio per share such that ATMI’s stockholders would own 49% of the pro forma combined company. Based on the closing price of Company A’s common stock on October 17, 2013, Company A’s proposal represented a purchase price of approximately $28.94 per share, or approximately a 3.1% premium to the closing price of the shares of ATMI common stock on October 17, 2013. Following receipt of the proposal, representatives of Barclays, after discussion with representatives of ATMI’s management, communicated to Company A that they would respond to the proposal after the next meeting of the board of directors.

During the last week of October 2013 through the first week of November 2013, three of the nine potential buyers that were sent a first round process letter, including Entegris, submitted an initial indication of interest for a potential acquisition of ATMI’s Microelectronics business. Entegris submitted an initial indication of interest for an all cash transaction with an enterprise value range of $800 million to $900 million. One of the potential buyers in the process, which we refer to as Company B, submitted an initial indication of interest for an all cash transaction with an enterprise value range of $875 million to $1,025 million. Another potential buyer in the process, which we refer to as Company C, submitted an initial indication of interest for an all cash transaction with an enterprise value of $850 million. The remaining parties either expressed an interest in only a very specific business line within the Microelectronics business or declined to move forward with the process.

On November 1, 2013, a story was published in various media outlets that ATMI had hired Barclays to explore strategic alternatives for ATMI. In response to the story, ATMI issued a press release confirming that it was exploring strategic alternatives and that it had engaged Barclays.

On November 5, 2013, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. Representatives of Barclays and Weil provided an update to the board of directors on the processes for potential sales of ATMI’s Microelectronics business and its Life Sciences business. In particular, representatives from Barclays reviewed with the board of directors the “merger-of-equals” proposal from Company A and noted that the proposal was for a stock-for-stock merger as opposed to an all cash transaction. In addition, the representatives from Barclays noted the low premium implied by Company A’s proposal, which was not unusual for a merger-of-equals transaction. The board of directors, following discussions with representatives of ATMI’s management, Barclays and Weil, determined that the proposed “merger of equals” transaction was not in the best interests of the ATMI stockholders, especially given the low implied premium and the fact that the sales processes for both ATMI’s Microelectronics business and its Life Sciences business appeared to be promising. At the conclusion of the meeting, the board of directors determined that ATMI should continue to pursue the separate sales processes for ATMI’s Microelectronics business and its Life Sciences business and not to pursue the “merger of equals” proposal from Company A. The board of directors also instructed Barclays to inform Company A of its decision. Subsequently, representatives of Barclays informed Company A that ATMI would not be interested in pursuing a “merger of equals” transaction at this time but that, should ATMI’s view change at a later time, representatives of Barclays would contact Company A.

Also, on November 5, 2013, a company, which we refer to as Company D, which had not been part of the initial list of potential strategic buyers identified by representatives of ATMI’s management and Barclays because, based on publicly available information, it did not seem to have a meaningful microelectronics business, communicated to representatives of Barclays that, after reading the November 1, 2013 press release confirming that ATMI was exploring strategic alternatives, Company D was interested in participating in the Microelectronics business sales process. On November 8, 2013, representatives of Barclays, on behalf of ATMI, sent to Company D the same first round process letter previously provided to other potential buyers. On November 12, 2013, Company D signed a confidentiality agreement with respect to the Microelectronics

27

Table of Contents

business sales process with the same standstill restrictions as were included in the other confidentiality agreements that would terminate upon the signing of a transaction for the sale of ATMI. On that same day, Company D attended a presentation regarding ATMI’s Microelectronics business conducted by representatives of ATMI’s management.

During the period from November 7, 2013, through November 11, 2013, Entegris, Company B and Company C attended presentations regarding ATMI’s Microelectronics business conducted by representatives of ATMI’s management. Starting at this time, the potential buyers were also granted access to an online data room containing non-public information about ATMI’s Microelectronics business, including certain projections prepared by ATMI’s management. See the section of this proxy statement entitled “— Certain Financial Forecasts.”

On November 13, 2013, a company that had previously been sent the first round process letter for the Microelectronics business, which we refer to as Company E, submitted a verbal indication of interest for an all cash transaction with an enterprise value of $800 million. As part of its submission, Company E communicated to representatives of Barclays that it would not be in a position to increase its purchase price materially from what it had included in its indication of interest. As a result, Company E was excluded from the final round process letter that was sent to potential buyers the following week.

Also on November 13, 2013, the board of directors, in light of the two simultaneous sales processes for the Microelectronics business and its Life Sciences business, created a transaction committee comprised of Messrs. Adley and Segall, together with Douglas Neugold (Chairman of the Board and Chief Executive Officer of ATMI) to oversee the review of potential strategic alternatives, including reviewing the terms and conditions of any potential transaction and to regularly update the board of directors with respect to the status and terms of any potential transaction. None of the members of the transaction committee has any agreement, understanding or arrangement with Entegris for continued employment or service after the consummation of the merger.

On November 18, 2013, representatives of Barclays, on behalf of ATMI, sent a final round process letter to each of Entegris, Company B and Company C. The final round process letter requested that each potential buyer submit, by December 13, 2013, a final, written proposal for the acquisition of ATMI (assuming that the Life Sciences business has already been sold).

On November 19, 2013, Company D submitted an initial indication of interest for an all cash transaction with an enterprise value range of $800 million to $900 million. Based on this indication of interest, Company D was invited to join the final round of the Microelectronics business sales process and was sent the final round process letter.

On November 26, 2013, Company D attended a presentation regarding ATMI’s Microelectronics business conducted by representatives of ATMI’s management.

On November 27, 2013, a draft merger agreement, prepared by representatives of Weil on behalf of ATMI, was made available to each of the final round bidders for the Microelectronics business.

On December 4, 2013, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. At the meeting, representatives of Barclays and Weil provided an update to the board of directors on the processes for the potential sales of ATMI’s Microelectronics business and its Life Sciences business. Representatives of Barclays noted that the potential buyers for the Microelectronics business had requested, as part of their due diligence, sufficient time to review the definitive agreement with respect to the sale of the Life Sciences business. As a result, the representatives of Barclays recommended, and the board of directors approved, an extension of the bid deadline for the Microelectronics business sales process from December 13, 2013 to early January 2014.

On December 6, 2013, representatives of Barclays, on behalf of ATMI, sent a letter to each of the four remaining potential buyers in the Microelectronics business sales process informing them that the bid deadline had been extended to January 7, 2014.

28

Table of Contents

On December 11, 2013, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. At the meeting, representatives of Barclays and Weil provided an update to the board of directors on the processes for the potential sales of ATMI’s Microelectronics business and its Life Sciences business. Further, representatives of Barclays provided an overview of the initial indications of interest that had been received with respect to the Microelectronics business sales process and an update on the due diligence activities of the remaining bidders in the process.

On December 22, 2013, ATMI announced that it had entered into a definitive agreement with Pall Corporation with respect to the sale of its Life Sciences business for a purchase price of $185 million in cash, subject to certain adjustments for working capital. Prior to its execution, the board of directors approved the definitive agreement and declared it to be advisable, fair to and in the best interests of ATMI and its stockholders.

On December 26, 2013, Company D informed representatives of Barclays that it would be withdrawing from the Microelectronics business sales process citing its revised analysis of the growth profile of the microelectronics industry generally and ATMI’s growth assumptions and the fact that, in its view, synergies would be difficult to achieve.

In early January 2014, in response to requests from certain of the remaining bidders in the Microelectronics business sales process, representatives of Barclays, on behalf of ATMI, informed each of the remaining bidders that the bid deadline would be moved to January 16, 2014.

On January 8, 2014, Company B informed representatives of Barclays that it would not be submitting a final bid. Company B explained that it had revised its view on the value of ATMI’s Microelectronics business and believed that its final bid would not be competitive in light of the then-current share price of ATMI but that Barclays should reach out to Company B should it think that it may be competitive in the process at a later stage. Representatives of Barclays informed representatives of ATMI’s management of this development, including Mr. Neugold, who subsequently informed the other members of the transaction committee and other directors.

On January 15, 2014, Company C informed representatives of Barclays that it would not be submitting a final bid. Company C explained that its ongoing work with respect to evaluating other opportunities in a different industry sector precluded it from pursuing ATMI’s Microelectronics business at this time and that while it believed ATMI could be a good strategic fit, it was not in a position to execute a transaction with ATMI at this time. Representatives of Barclays informed representatives of ATMI’s management of this development, including Mr. Neugold, who subsequently informed the other members of the transaction committee and other directors.

On January 16, 2014, Entegris submitted a proposal, including a mark-up of the merger agreement that had been provided to bidders and a draft debt commitment letter, for the acquisition of ATMI for cash at an enterprise value of $830 million. Based on certain assumptions with respect to ATMI’s projected cash balances, debt and other obligations, Barclays advised ATMI’s management that Entegris’ proposal represented a proposed transaction at approximately $32.37 per share. In addition, the terms of Entegris’ proposal included (1) a reduction in the proposed purchase price if ATMI’s unrestricted cash balance at closing was below a specified amount, (2) a “reverse” termination fee equal to 5% of the transaction value payable by Entegris to ATMI under certain circumstances if Entegris was unable to consummate the transaction due to its failure to obtain the contemplated debt financing and (3) a termination fee equal to 4% of the transaction value payable by ATMI to Entegris if ATMI were to terminate the transaction under certain circumstances to accept a “superior proposal.” Representatives of Barclays informed representatives of ATMI’s management of this development, including Mr. Neugold, who subsequently informed the other members of the transaction committee and other directors.

On January 20, 2014, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. At the meeting, representatives of Barclays presented the board of

29

Table of Contents

directors with a review of the Microelectronics business sales process, including an analysis of the proposal from Entegris. Members of the board of directors discussed the proposal in comparison to other potential strategic alternatives available to ATMI, including remaining a standalone company and using excess cash (including the projected after-tax cash proceeds from the sale of the Life Sciences business) for a special dividend or a share repurchase program. As part of this discussion, representatives of Barclays reviewed with the board of directors a preliminary valuation analysis of ATMI (excluding the Life Sciences business and including the projected after-tax cash proceeds from the sale of the Life Sciences business). The board of directors also discussed with representatives from ATMI’s management and Barclays potential headwinds in the microelectronics industry and the achievability of ATMI management’s financial projections. The board of directors concluded the meeting by requesting that Barclays prepare a more detailed analysis of Entegris’ proposal as compared to other potential strategic alternatives potentially available to ATMI, including maintaining the status quo as a stand-alone company, and that ATMI’s management prepare a set of financial projections that represented a downside sensitivity to the Budget case. See the section of this proxy statement entitled “—Certain Financial Forecasts.”

On January 22, 2014, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. At the meeting, representatives of Barclays reviewed with the board of directors various potential strategic alternatives available to ATMI, including a sale of ATMI to Entegris for cash, a “merger of equals” transaction with Company A, growing ATMI through strategic acquisitions or remaining a standalone company and using excess cash (including the projected after-tax cash proceeds from the sale of the Life Sciences business) for a special dividend or a share repurchase program. As part of this discussion, representatives of Barclays reviewed with the board of directors a preliminary valuation analysis of ATMI (excluding the Life Sciences business and including the projected after-tax cash proceeds from the sale of the Life Sciences business). At the conclusion of the discussion, the board of directors determined that Entegris’ current proposal was insufficient and instructed the representatives of Barclays to request that Entegris submit a higher, revised bid on a per share basis. In addition, the board of directors also instructed the representatives of Barclays to contact Company A, Company B and Company C to see if they had any renewed interest in making a proposal to acquire ATMI. In particular, with respect to Company B and Company C, Barclays was instructed to guide each of those potential buyers to a price of at least $35.00 per share of ATMI common stock.

On the evening of January 22, 2014, representatives of Barclays, on behalf of ATMI, contacted representatives of Entegris and requested that Entegris submit a higher, revised bid on a per share basis no later than the close of business on January 23, 2014.

On January 23, 2014, representatives of Entegris contacted representatives of Barclays with a revised bid of $34.00 per share in cash. The revised bid was also subject to several conditions, including the completion of confirmatory due diligence, obtaining exclusivity and a potential purchase price adjustment if ATMI did not have a specified amount of unrestricted cash as of March 31, 2014. The representatives of Entegris characterized the proposal as Entegris’ “best and final” offer.

On January 24, 2014, representatives of Barclays, on behalf of ATMI and in accordance with the instructions from the board of directors at the meeting on January 22, 2014, contacted each of Company A, Company B and Company C to solicit any renewed interest in a potential acquisition of ATMI. Each of Company A and Company C stated that they would get back to representatives of Barclays over the next few days. Company B communicated that it would not be able to bid for ATMI at the $35.00 per share price that the representatives of Barclays had indicated.

Also, on January 24, 2014, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. At the meeting, representatives of Weil reviewed with the board of directors its fiduciary duties, including the legal standards applicable to its decisions with respect to a potential sale of ATMI. Representatives of Barclays then updated the board of directors with respect to the conversations that they had had with each of Company A, Company B and Company C and Entegris’ revised proposal to acquire ATMI for $34.00 per share in cash. The board of directors, together with the representatives of ATMI’s management,

30

Table of Contents

Barclays and Weil, then discussed the various potential strategic alternatives available to ATMI as compared to Entegris’ revised proposal, including a “merger of equals” transaction with Company A, growing ATMI through strategic acquisitions or remaining a standalone company and using excess cash (including the projected after-tax cash proceeds from the sale of the Life Sciences business) for a special dividend or a share repurchase program. As part of this discussion, representatives of Barclays reviewed with the board of directors a preliminary valuation analysis of ATMI (excluding the Life Sciences business and including the projected after-tax cash proceeds from the sale of the Life Sciences business). At the conclusion of the meeting, the board of directors authorized representatives of Barclays to make a counter-offer to Entegris at $35.00 per share in cash.

On the evening of January 24, 2014, representatives from Barclays, on behalf of ATMI, communicated to representatives of Entegris a counter-offer to sell ATMI for $35.00 per share in cash.

On January 27, 2014, representatives of Entegris responded to representatives of Barclays that it would not be able to offer a price above $34.00 per share and that the $34.00 per share price remained its “best and final” offer.

During this time, Company A and Company C responded to the previous inquiries by representatives of Barclays. Company A communicated that it would submit a proposal later in the week. Company C communicated that while a price range of $35.00 per share was potentially achievable, it would not be in a position to sign a transaction for at least another three to six months because, as it had stated earlier, it was currently evaluating other opportunities in a different industry sector.

Also, on January 27, 2014, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. At the meeting, representatives of Barclays informed the board of directors that Entegris had declined to increase its proposal and $34.00 per share in cash remained its “best and final” offer. In addition, Barclays updated the board of directors regarding the conversations it had had with each of Company A and Company C. The board of directors, together with the representatives of ATMI’s management, Barclays and Weil, then discussed Entegris’ proposal. In particular, the board of directors were concerned with (1) the purchase price adjustment related to ATMI’s unrestricted cash balance, (2) the risk associated with Entegris not obtaining the debt financing necessary to fund the proposed purchase price, including the size of the 5% of transaction value “reverse” termination fee proposed by Entegris and (3) the size of the 4% of transaction value termination fee payable by ATMI to Entegris if ATMI were to terminate the transaction under certain circumstances to accept a “superior proposal.” At the conclusion of the meeting, the board of directors authorized management, Barclays and Weil to continue to pursue a sale of ATMI to Entegris at $34.00 per share in cash but to seek improvements to the terms of the transaction with respect to (1) the price adjustment related to ATMI’s unrestricted cash balance, (2) the “reverse” termination fee proposed by Entegris in favor of a remedy of specific performance and (3) decreasing the size of the termination fee from the 4% of transaction value termination fee proposed by Entegris to closer to the 2% of transaction value as proposed by ATMI in the initial draft of the merger agreement.

Over the next several days until February 3, 2014, representatives of ATMI’s management and Barclays and Weil and representatives of Entegris’s management and financial and legal advisors negotiated the outstanding terms of the transaction, particularly the terms outlined above, and exchanged drafts of the merger agreement. During this time, the representatives of ATMI’s management and Barclays and Weil kept the members of the transaction committee and ATMI’s other directors informed of the status of the negotiations and obtained guidance on negotiating positions.

On January 28, 2014, Company A verbally communicated to representatives of Barclays that it was prepared to make a proposal to acquire ATMI for $33.00 per share consisting of a mix of approximately 85% cash and 15% Company A common stock. After Barclays conveyed to Company A that such an offer would be insufficient to make Company A’s bid competitive in the process, Company A verbally communicated that it was prepared to submit a revised proposal. Barclays requested that Company A submit its revised proposal in writing.

On January 30, 2014, Company A submitted to ATMI a written proposal for the acquisition of ATMI at an indicated purchase price of $30.00 to $40.00 per share, of which (1) $17.00 to $27.00 per share in cash would be

31

Table of Contents

paid by Company A, (2) $5.50 per share would be paid in shares of Company A common stock and (3) $7.50 per share in cash would be paid in the form of a special dividend by ATMI. In addition, Company A’s proposal was subject to due diligence, which Company A anticipated would take a period of 21 days to complete. Representatives of ATMI’s management reviewed Company A’s proposal with representatives of Barclays and Weil, and informed the members of the transaction committee. ATMI’s management, after receiving input from the members of the transaction committee and consulting with representatives of Barclays and Weil, concluded that the price range of Company A’s proposal was too uncertain and the due diligence period was too long for ATMI to risk losing the proposed transaction with Entegris, which had previously indicated that it was unwilling to delay the process further. Representatives from Barclays, on behalf of ATMI, informed Company A that it would need to submit a more precise proposal if it wanted the proposal to be considered further by ATMI.

On February 1, 2014, Company A submitted to ATMI a revised written proposal for the acquisition of ATMI at a purchase price of $33.00 to $40.00 per share, of which (1) $20.00 to $27.00 per share in cash would be paid by Company A, (2) $5.50 per share would be paid in shares of Company A common stock and (3) $7.50 per share in cash would be paid in the form of a special dividend by ATMI. Company A’s proposal continued to be subject to a 21 day due diligence process. Representatives of ATMI’s management reviewed Company A’s proposal with representatives of Barclays and Weil, and informed the members of the transaction committee.

On February 3, 2014, the board of directors held a meeting at which representatives of ATMI’s management, Barclays and Weil were present. The representatives of Weil began the meeting with a review of the fiduciary duties of the board of directors, including the legal standards applicable to its decisions with respect to a potential sale of ATMI. The representatives of Weil then provided an overview of the key terms of the revised merger agreement that had been negotiated with Entegris including (1) that the consideration of $34.00 per share in cash would be fixed and would not be subject to adjustments based on ATMI’s unrestricted cash balance, (2) Entegris would owe ATMI a “reverse” termination fee equal to $100 million (approximately 8.7% of the transaction value) if Entegris failed to consummate the transaction in certain circumstances due to a failure to obtain the contemplated debt financing and (3) ATMI would owe Entegris a termination fee equal to $30 million (approximately 2.6% of the transaction value) in certain circumstances where ATMI terminated the merger agreement to enter into a “superior proposal.” During the meeting, the board of directors discussed the proposal made by Company A on February 1, 2014, and concluded that Company A’s proposal remained too uncertain with respect to price and timing to risk losing the transaction with Entegris. The representatives of Weil also noted that ATMI would be permitted under the terms of the merger agreement, to furnish confidential information to, and conduct negotiations with, any third party, including Company A, that makes an unsolicited proposal to acquire ATMI, and ultimately terminate the merger agreement to accept a “superior proposal,” subject to the limitations and requirements contained in the merger agreement, including the right of Entegris to “match” such “superior proposal” and the payment to Entegris of the $30 million termination fee. The representatives of Barclays then made a presentation with respect to the proposed offer from Entegris of $34.00 per share in cash. The representatives of Barclays noted that the written materials distributed to the board of directors prior to the meeting contained preliminary 2013 year-end information, that immediately prior to the meeting representatives of ATMI’s management had provided Barclays with final 2013 year-end information and that, after the meeting, Barclays would circulate to the board of directors revised materials that reflect such final 2013 year-end information. Also, at the meeting, Barclays rendered its oral opinion, which opinion was subsequently confirmed in a written opinion dated February 4, 2014, to the ATMI board of directors to the effect that, as of that date and based upon and subject to the qualifications, limitations and assumptions stated in its written opinion, the merger consideration of $34.00 per share of ATMI common stock to be offered to the stockholders of ATMI in the merger was fair, from a financial point of view, to such stockholders (a copy of the written opinion of Barclays is attached to this proxy statement as Annex B). After careful deliberation, including consideration of the factors described in the section of this proxy statement entitled “— Reasons for the Merger; Recommendation of Our Board of Directors,” the board of directors, unanimously (1) approved the execution, delivery, and performance of the merger agreement, (2) determined that entering into the merger agreement is fair to, and in the best interests of ATMI and its stockholders, (3) declared the merger agreement and the merger advisable, and (4) subject to its fiduciary obligations, resolved to recommend that ATMI’s stockholders adopt the merger agreement.

32

Table of Contents

Through the night of February 3, 2014 and into the morning of February 4, 2014, the parties worked to finalize the terms of the merger agreement in accordance with the terms discussed with the board of directors and, on the morning of February 4, 2014, the parties executed and delivered the merger agreement and Entegris delivered the fully executed debt commitment letter contemplated by the merger agreement. Prior to the opening of trading in the U.S. securities markets, ATMI and Entegris issued a joint press release announcing the transaction.

Reasons for the Merger; Recommendation of Our Board of Directors

Reasons for the Merger

Our board of directors, with the advice and assistance of our management and legal and financial advisors, at a meeting on February 3, 2014, carefully evaluated the proposed merger, including the terms and conditions of the merger agreement. Our board of directors unanimously (1) approved the execution, delivery, and performance of the merger agreement, (2) determined that entering into the merger agreement is fair to, and in the best interests of, ATMI and its stockholders, (3) declared the merger agreement and the merger advisable, and (4) subject to its fiduciary obligations, resolved to recommend that ATMI’s stockholders adopt the merger agreement.

In the course of reaching its determination, our board of directors consulted with our management and its legal and financial advisors and considered a number of substantive factors and potential benefits of the merger. Our board of directors believed that, taken as a whole, the following factors supported its decision to approve the proposed merger:

33

Table of Contents

In addition, the board of directors was aware of and considered the interests that certain individuals, including our directors and executive officers, may have with respect to the merger that may differ from, or may be in addition to, their interests as stockholders of ATMI, as described in the section of this proxy statement entitled “— Interests of Certain Persons in the Merger.”

Our board of directors also considered potential risks or negative factors relating to the merger, including but not limited to the following:

34

Table of Contents

The foregoing discussion summarizes certain material factors considered by the board of directors in its consideration of the merger. In view of the wide variety of factors considered by the board of directors, and the complexity of these matters, the board of directors did not find it practicable to quantify or otherwise assign relative weights to the foregoing factors. In addition, individual members of the board of directors may have assigned different weights to various factors. Our board of directors concluded that the potentially negative factors associated with the merger agreement were substantially outweighed by the opportunity for ATMI’s stockholders to realize a premium on the value of their shares of common stock. Accordingly, our board of directors, by unanimous vote, (1) approved the execution, delivery, and performance of the merger agreement, (2) determined that entering into the merger agreement is fair to, and in the best interests of, ATMI and its stockholders, (3) declared the merger agreement and the merger advisable, and (4) subject to its fiduciary obligations, resolved to recommend that ATMI’s stockholders adopt the merger agreement.

Recommendation of our Board of Directors

Our board of directors recommends that you vote “FOR” the proposal to adopt the merger agreement and approve the merger.

Opinion of ATMI’s Financial Advisor

ATMI engaged Barclays to act as its financial advisor with respect to a possible sale of ATMI. On February 3, 2014, Barclays rendered its oral opinion, which opinion was subsequently confirmed in a written opinion dated February 4, 2014, to the ATMI board of directors to the effect that, as of that date and based upon and subject to the qualifications, limitations and assumptions stated in its written opinion, the merger consideration of $34.00 per share of ATMI common stock to be offered to the stockholders of ATMI in the merger was fair, from a financial point of view, to such stockholders.

The full text of Barclays’ written opinion, dated as of February 4, 2014, is attached as Annex B to this proxy statement. Barclays’ opinion sets forth, among other things, the assumptions made, procedures followed, factors considered and limitations upon the review undertaken by Barclays in rendering its opinion. ATMI encourages you to read the opinion carefully in its entirety. The following is a summary of Barclays’ opinion and the methodology that Barclays used to render its opinion. This summary is qualified in its entirety by reference to the full text of the opinion.

35

Table of Contents

Barclays’ opinion, the issuance of which was approved by Barclays’ Valuation and Fairness Opinion Committee, is addressed to the ATMI board of directors, addresses only the fairness, from a financial point of view, of the merger consideration of $34.00 per share of ATMI common stock to be offered to the stockholders of ATMI and does not constitute a recommendation to any stockholder of ATMI as to how such stockholder should vote with respect to the merger or any other matter. The terms of the merger were determined through arm’s-length negotiations between ATMI and Entegris and were approved by the ATMI board of directors. Barclays did not recommend any specific amount or form of consideration to ATMI or that any specific amount or form of consideration constituted the only appropriate consideration for the merger. Barclays was not requested to opine as to, and its opinion does not in any manner address, ATMI’s underlying business decision to proceed with or effect the merger or the likelihood of the consummation of the merger. Barclays’ opinion did not address the relative merits of the merger as compared to any other transaction or business strategy in which ATMI might engage. In addition, Barclays expressed no opinion on, and its opinion does not in any manner address, the fairness of the amount or the nature of any compensation to any officers, directors or employees of any parties to the merger, or any class of such persons, relative to the merger consideration of $34.00 per share of ATMI common stock to be offered to the stockholders of ATMI in the merger. No limitations were imposed by the ATMI board of directors upon Barclays with respect to the investigations made or procedures followed by it in rendering its opinion.

In arriving at its opinion, Barclays, among other things:

In arriving at its opinion, Barclays assumed and relied upon the accuracy and completeness of the financial and other information used by Barclays without any independent verification of such information (and did not assume responsibility or liability for any independent verification of such information). Barclays also relied upon

36

Table of Contents

the assurances of management of ATMI that they were not aware of any facts or circumstances that would make such information inaccurate or misleading. With respect to the financial projections of ATMI, upon the advice of ATMI, Barclays assumed that such projections were reasonably prepared on a basis reflecting the best currently available estimates and judgments of the management of ATMI as to ATMI’s future financial performance. In arriving at its opinion, Barclays assumed no responsibility for and expressed no view as to any such projections or estimates or the assumptions on which they were based. In arriving at its opinion, Barclays did not conduct a physical inspection of the properties and facilities of ATMI and did not make or obtain any evaluations or appraisals of the assets or liabilities of ATMI. Barclays’ opinion was necessarily based upon market, economic and other conditions as they existed on, and could be evaluated as of, the date of its opinion. Barclays assumed no responsibility for updating or revising its opinion based on events or circumstances that may have occurred after February 3, 2014.

Barclays has assumed that the executed merger agreement would conform in all material respects to the last draft reviewed by Barclays. In addition, Barclays has assumed the accuracy of the representations and warranties contained in the merger agreement and all agreements related thereto. Barclays has also assumed, upon the advice of ATMI, that all material governmental, regulatory and third party approvals, consents and releases for the merger will be obtained within the constraints contemplated by the merger agreement and that the merger will be consummated in accordance with the terms of the merger agreement without waiver, modification or amendment of any material term, condition or agreement thereof. Barclays did not express any opinion as to any tax or other consequences that might result from the merger, nor does its opinion address any legal, tax, regulatory or accounting matters, as to which it understood that ATMI had obtained such advice as ATMI deemed necessary from qualified professionals.

In connection with rendering its opinion, Barclays performed certain financial, comparative and other analyses as summarized below. In arriving at its opinion, Barclays did not ascribe a specific range of values to the shares of ATMI common stock but rather made its determination as to fairness, from a financial point of view, to ATMI’s stockholders of the consideration to be offered to such stockholders in the merger on the basis of various financial and comparative analyses. The preparation of a fairness opinion is a complex process and involves various determinations as to the most appropriate and relevant methods of financial and comparative analyses and the application of those methods to the particular circumstances. Therefore, a fairness opinion is not readily susceptible to summary description.

In arriving at its opinion, Barclays did not attribute any particular weight to any single analysis or factor considered by it but rather made qualitative judgments as to the significance and relevance of each analysis and factor relative to all other analyses and factors performed and considered by it and in the context of the circumstances of the particular transaction. Accordingly, Barclays believes that its analyses must be considered as a whole, as considering any portion of such analyses and factors, without considering all analyses and factors as a whole, could create a misleading or incomplete view of the process underlying its opinion.

The following is a summary of the material financial analyses used by Barclays in preparing its opinion to the ATMI board of directors. Certain financial analyses summarized below include information presented in tabular format. In order to fully understand the financial analyses used by Barclays, the tables must be read together with the text of each summary, as the tables alone do not constitute a complete description of the financial analyses. In performing its analyses, Barclays made numerous assumptions with respect to industry performance, general business and economic conditions and other matters, many of which are beyond the control of ATMI or any other parties to the merger. None of ATMI, Entegris, Merger Sub, Barclays or any other person assumes responsibility if future results are materially different from those discussed. Any estimates contained in these analyses are not necessarily indicative of actual values or predictive of future results or values, which may be significantly more or less favorable than as set forth below. In addition, analyses relating to the value of the businesses do not purport to be appraisals or reflect the prices at which the businesses may actually be sold.

37

Table of Contents

In performing its financial analyses summarized below and in arriving at its opinion, Barclays utilized and relied upon the Budget case financial projections, which had been prepared by ATMI’s management on bases reflecting the best currently available estimates and judgments of ATMI’s management as to the future financial performance of ATMI.

In addition, solely for reference purposes, Barclays also performed a selected comparable company analysis and a discounted cash flow analysis (as described below) utilizing the Business Model case and the Conservative case financial projections. For further information regarding these financial projections, see the section of this proxy statement entitled “— Certain Financial Forecasts.”

Analysis of Implied Premiums and Multiples

Barclays analyzed the implied premiums based on the merger consideration of $34.00 per share of ATMI common stock as compared to the following:

The results of this analysis are summarized in the following table:

Barclays also analyzed the implied premiums based on the merger consideration of $34.00 per share of ATMI common stock as compared to certain recent trading prices of ATMI common stock set forth below, in each case, adjusted to exclude ATMI’s after-tax net cash position pro forma for the sale of the Life Sciences business pursuant to the Life Sciences SAPA estimated to be approximately $8.35 per share of ATMI common stock. The results of this analysis are summarized in the following table:

38

Table of Contents

Selected Comparable Company Analysis

In order to assess how the public market values shares of similar publicly traded companies, Barclays reviewed and compared specific financial and operating data relating to ATMI with selected companies that serve as suppliers in the microelectronics and semiconductor manufacturing industry that Barclays deemed comparable to ATMI. The selected comparable companies were:

Barclays calculated and compared various financial multiples and ratios of ATMI and the selected comparable companies. As part of its selected comparable company analysis, Barclays calculated and analyzed, among other things, each company’s enterprise value to historical and projected earnings before interest, taxes, depreciation and amortization, or EBITDA, for calendar years 2013 and 2014. The enterprise value of each company was obtained by adding its short and long-term debt to the sum of its equity value, the value of any preferred stock (at liquidation value) and the book value of any minority interest, and subtracting its cash and cash equivalents. All of these calculations were performed, and based on publicly available financial data (including I/B/E/S Consensus), ATMI management’s financial projections and closing prices, as of February 3, 2014. The results of this selected comparable company analysis are summarized below:

Enterprise Value as a Multiple of Calendar Year 2013 Estimated EBITDA

Barclays selected the comparable companies listed above because of similarities in one or more business or operating characteristics with ATMI. However, because no selected comparable company is exactly the same as ATMI, Barclays believed that it was inappropriate to, and therefore did not, rely solely on the quantitative results of the selected comparable company analysis. Accordingly, Barclays also made qualitative judgments concerning differences between the business, financial and operating characteristics and prospects of ATMI and the selected comparable companies that could affect the public trading values of each in order to provide a context in which to consider the results of the quantitative analysis. These qualitative judgments related primarily to the differing sizes, growth prospects, profitability levels and degree of operational risk between ATMI and the companies included in the selected company analysis.

Based upon these judgments, Barclays selected a range of 10.0x to 11.0x ATMI’s calendar year 2013 EBITDA, adjusted to take into account the sale of the Life Sciences business pursuant to the Life Sciences SAPA, or 2013PF EBITDA, and 8.5x to 9.5x ATMI’s estimated calendar year 2014 EBITDA, or 2014E EBITDA, based on the Budget case to calculate a range of implied prices per share of ATMI. The selected

39

Table of Contents

comparable company analysis yielded an implied valuation range for shares of ATMI common stock of $33.25 to $35.75 per share using 2013PF EBITDA, and $32.25 to $35.00 per share using 2014E EBITDA (per share values were rounded to the nearest $0.25 increment), in each case, compared to the merger consideration of $34.00 per share of ATMI common stock.

In addition, solely for reference purposes, Barclays also used the range of 8.5x to 9.5x ATMI’s 2014E EBITDA based on the Business Model case and the Conservative case to calculate a range of implied prices per share of ATMI common stock. This analysis yielded an implied valuation range for ATMI common stock of $36.00 to $39.25 per share based on the Business Model case, and $30.75 to $33.25 per share using the Conservative case (per share values were rounded to the nearest $0.25 increment), in each case, compared to the merger consideration of $34.00 per share of ATMI common stock.

Selected Precedent Transaction Analysis

Barclays reviewed and compared the purchase prices and financial multiples paid in selected other transactions involving target companies in the microelectronics and semiconductor manufacturing industry that Barclays, based on its experience with merger and acquisition transactions, deemed relevant. Barclays chose such transactions based on, among other things, the similarity of the applicable target companies in the transactions to ATMI with respect to the size, mix, margins and other characteristics of their businesses. The following table sets forth the transactions analyzed based on such characteristics and the date each transaction was announced:

Barclays calculated and compared various financial multiples and ratios of ATMI and the target company in each of the selected precedent transactions listed above. As part of its selected precedent transactions analysis, Barclays calculated, among other things, the ratio of the target company’s enterprise value to its estimated last twelve months EBITDA as of the announcement date of such transaction, referred to below as EV/LTM EBITDA. The results of this selected precedent transactions company analysis are summarized below:

The reasons for and the circumstances surrounding each of the selected precedent transactions analyzed were diverse and there are inherent differences in the business, operations, financial conditions and prospects of ATMI and the companies included in the selected precedent transaction analysis. Accordingly, Barclays believed that a purely quantitative selected precedent transaction analysis would not be particularly meaningful in the context of considering the merger consideration of $34.00 per share of ATMI common stock in the merger.

40

Table of Contents

Barclays therefore made qualitative judgments concerning differences between the characteristics of the selected precedent transactions and the merger which would affect the acquisition values of the selected target companies and ATMI.

Based upon these judgments, Barclays selected a multiple range of 10.0x to 11.0x ATMI’s 2013PF EBITDA to calculate a range of implied prices per share of ATMI common stock. The selected precedent transactions analysis yielded an implied valuation range for ATMI common stock of $33.25 to $35.75 per share (per share values were rounded to the nearest $0.25 increment), compared to the merger consideration of $34.00 per share of ATMI common stock.

Discounted Cash Flow Analysis

In order to estimate the present value of ATMI common stock, Barclays performed a discounted cash flow analysis of ATMI. A discounted cash flow analysis is a traditional valuation methodology used to derive a valuation of an asset by calculating the “present value” of estimated future cash flows of the asset. “Present value” refers to the current value of future cash flows or amounts and is obtained by discounting those future cash flows or amounts by a discount rate that takes into account macroeconomic assumptions and estimates of risk, the opportunity cost of capital, expected returns and other appropriate factors.

To calculate the estimated enterprise value of ATMI using the discounted cash flow method, Barclays added (i) ATMI’s projected after-tax unlevered free cash flows for fiscal years 2014 through 2018 based on the Budget case to (ii) the “terminal value” of ATMI as of December 31, 2018, and discounted such amount to its present value using a range of selected discount rates. The residual value of ATMI at the end of the forecast period, or “terminal value,” was estimated by selecting a range of terminal value multiples based on ATMI’s estimated EBITDA for the fiscal year period ended December 31, 2018 of 7.0x to 8.0x, which was derived by analyzing the results from the selected comparable company analysis and the historical trading multiples for ATMI and the selected comparable companies, and applying such range to the Budget case. A range of after-tax discount rates of 12.0% to 14.0% was selected based on an analysis of the weighted average cost of capital of ATMI and the selected comparable companies.

Combining the total present value of the estimated after-tax unlevered free cash flows and the present value of the terminal values resulted in a range of implied enterprise values for ATMI. Barclays then deducted estimated outstanding debt and added outstanding cash and equivalents as of December 31, 2013 to determine a range of implied equity values of ATMI as of that date. The cash balance estimated as of December 31, 2013 was adjusted to take into account estimated after-tax net proceeds from the sale of the Life Sciences business pursuant to the Life Sciences SAPA less certain expenses incurred by ATMI in connection with such sale, and the repatriation of certain foreign proceeds from that sale, and the proceeds from the settlement of certain equity investments.

This discounted cash flow analysis yielded the implied valuation ranges for ATMI common stock set forth in the table below (per share values were rounded to the nearest $0.25 increment), compared to the merger consideration of $34.00 per share of ATMI common stock:

The range of terminal value multiples described above implied a range of perpetuity growth rates for ATMI of 4.7% to 5.6%.

Barclays also performed a discounted cash flow analysis to calculate the estimated enterprise value of ATMI using ATMI’s projected after-tax unlevered free cash flows based on the Budget case and the range of after-tax discount rates each as described above, and perpetuity growth rates ranging from 4.5% to 5.0%. This

41

Table of Contents

range of perpetuity growth rates implied a range of terminal value multiples based on ATMI’s estimated EBITDA for the fiscal year period ended December 31, 2018 of 6.2x to 8.4x. Barclays then deducted projected outstanding debt and added outstanding cash and equivalents as of December 31, 2013 (as adjusted as described above) to determine a range of implied equity values of ATMI as of that date.

This discounted cash flow analysis yielded the implied valuation ranges for ATMI common stock set forth in the table below (per share values were rounded to the nearest $0.25 increment), compared to the merger consideration of $34.00 per share of ATMI common stock:

In addition, solely for reference purposes, Barclays also performed a discounted cash flow analysis using the range of discount rates, terminal value multiples and perpetuity growth rates described above and using ATMI’s projected after-tax unlevered free cash flows based on the Business Model case and the Conservative case. This discounted cash flow analysis yielded the implied valuation ranges for ATMI common stock set forth in the table below (per share values were rounded to the nearest $0.25 increment), compared to the merger consideration of $34.00 per share of ATMI common stock:

In rendering its opinion, Barclays also performed certain other analyses, as set forth below, which were solely for reference purposes and were not part of its fairness determination.

Historical Share Price Analysis

To illustrate the trend in the historical trading prices of ATMI common stock, Barclays considered historical data with regard to the trading prices of ATMI common stock for the period from February 3, 2013 to February 3, 2014. Barclays noted that during such period, the intraday trading price of ATMI common stock ranged from $20.00 to $30.50 (per share values were rounded to the nearest $0.25 increment).

Analyst Price Targets

Barclays reviewed the public market trading price targets for ATMI common stock prepared and published by securities research analysts as of February 3, 2014. These targets reflected each analyst’s undiscounted estimate of the future public market trading price for ATMI common stock. The public market trading price targets published by securities research analysts do not necessarily reflect current market trading prices for the shares and these estimates are subject to uncertainties, including future financial performance of ATMI and future financial market conditions. The equity analysts price targets for ATMI common stock ranged from $22.00 to $36.00 per share, with a median of $29.25.

General

Barclays is an internationally recognized investment banking firm and, as part of its investment banking activities, is regularly engaged in the valuation of businesses and their securities in connection with mergers and acquisitions, investments for passive and control purposes, negotiated underwritings, competitive bids, secondary

42

Table of Contents

distributions of listed and unlisted securities, private placements and valuations for estate, corporate and other purposes. The ATMI board of directors selected Barclays because of its qualifications, reputation and experience in the valuation of businesses and securities in connection with mergers and acquisitions generally.

Barclays is acting as financial advisor to ATMI in connection with the merger. As compensation for its services in connection with the merger, ATMI agreed to pay Barclays a fee of $750,000 upon the delivery of Barclays’ opinion. ATMI has also agreed to pay Barclays a fee estimated to be approximately $8.7 million upon consummation of the merger, against which the fee paid to Barclays in connection with its opinion will be credited. In addition, ATMI has agreed to reimburse Barclays’ expenses and indemnify Barclays for certain liabilities that may arise out of its engagement. Barclays has performed various investment banking and financial services for ATMI in the past, and expects to perform such services in the future, and has received, and expects to receive, customary fees for such services. Specifically, in the two years prior to the date of Barclays’ opinion, Barclays has served as financial advisor to ATMI in connection with the sale of its Life Sciences business pursuant to the Life Sciences SAPA for which ATMI has agreed to pay Barclays a fee of $1.7 million. In the two years prior to the date of Barclays’ opinion, Barclays has not performed any investment banking or financial services for Entegris.

Barclays and its affiliates engage in a wide range of businesses from investment and commercial banking, lending, asset management and other financial and non-financial services. In the ordinary course of its business, Barclays and affiliates may actively trade and effective transactions in the equity, debt and/or other securities (and any derivatives thereof) and financial instruments (including loans and other obligations) of ATMI and Entegris for its own account and for the accounts of its customers and, accordingly, may at any time hold long or short positions and investments in such securities and financial instruments.

Certain Financial Forecasts

ATMI does not as a matter of general practice publicly disclose financial projections due to, among other reasons, the unpredictability of the underlying assumptions and estimates inherent in preparing financial projections. In evaluating ATMI’s strategic alternatives, including a potential transaction with Entegris, ATMI’s management prepared three forecasts of ATMI’s results of operations, a “Business Model” case forecast, a “Budget” case forecast and a “Conservative” case forecast (referred to collectively in this proxy statement as the financial forecasts) and provided them to the ATMI board of directors, its advisors and, as specified below, to Entegris and other potential buyers of the Company. The financial forecasts constitute forward-looking statements. See “Cautionary Statement Concerning Forward-Looking Information.”

This summary of the financial forecasts is not provided to influence your decision regarding whether to vote for the adoption of the merger agreement, but is only being included because such financial forecasts were made available to the ATMI board of directors and its advisors in evaluating ATMI’s strategic alternatives, including a potential transaction with Entegris, and, as specified below, to Entegris and other potential buyers of the Company. The inclusion of this information in this proxy statement should not be regarded as an indication that the ATMI board of directors or its advisors or any other person considered, or now considers, the financial forecasts to be a reliable prediction of actual future results, and the financial forecasts should not be relied upon as such. ATMI’s internal financial projections, upon which the financial forecasts were based, are subjective in many respects. There can be no assurance that the financial forecasts will be realized or that actual results will not be significantly higher or lower than projected. The financial forecasts also cover multiple years and such information by its nature becomes subject to greater uncertainty with each successive year. Economic and business environments may change quickly, which adds an additional significant level of uncertainty as to whether the results portrayed in the financial forecasts will be achieved. As a result, the inclusion of the financial forecasts in this proxy statement does not constitute an admission or representation by ATMI that the information is material. Readers of this proxy statement are cautioned not to place undue reliance on the financial forecasts set forth below.

43

Table of Contents

Summary of Financial Forecasts

The following is a summary of the financial forecasts prepared by ATMI’s management and provided to the ATMI board of directors, its advisors and, only to the extent specified below, to Entegris and other potential buyers of the Company:

Business Model Case

The Business Model case was prepared by ATMI’s management in July 2013. The Business Model case was based on certain assumptions, including the following: improvements in ATMI’s growth and profitability as a result of, among other things, an improving semiconductor industry with modestly higher wafer starts growth, margin expansion through the introduction of higher margin new products and the localization of manufacturing activities, customer ramps at new advanced nodes, increased penetration at key accounts and subsequent wins at advanced nodes, and the rationalization of ATMI’s cost structure. The Business Model case was made available to Entegris and other potential buyers of the Company.

Budget Case

The Budget case was prepared by ATMI’s management on or about January 17, 2014. The Budget case was based on the 2014 budget approved by the ATMI board of directors in December 2013 and excludes ATMI’s Life Sciences business and the shared services related to the Life Sciences business. The Budget case, as compared to the Business Model case, reflected an updated, more conservative outlook for the semiconductor industry generally and the growth and profitability of ATMI in particular. The Budget case assumed growth rates for 2015-2018 to be in line with estimated growth rates for comparable public companies and gross margin improvement driven by a contribution margin on incremental revenues and resource efficiency mix. The Budget case reflected the best currently available estimates and judgments of ATMI’s management as to the future financial performance of ATMI. The 2014 budget, upon which the Budget case was prepared (but not the Budget case itself), was made available to Entegris and other potential buyers of the Company.

Conservative Case

The Conservative case was prepared by ATMI’s management on or about January 20, 2014. The Conservative case reflected a downside sensitivity to the Budget case. Specifically, the Conservative case incorporated a number of factors that could potentially adversely impact ATMI’s results, including: a deteriorating wafer start environment in 2014 and, consequently, a conservative growth rate of approximately 4% per year; price declines continuing through the projection period in line with the pricing figures from 2013; and ATMI’s resetting of incentive compensation targets, including incentive compensation payments in 2014 to be based on achievement of only individual strategic objectives (approximately 20% of the overall incentive compensation target amount) and incentive compensation targets in 2015 to be reset to 100%.

Because our financial forecasts were developed for ATMI on a standalone basis without giving effect to the merger, our financial forecasts do not reflect any effects of the merger or any changes to our operations or strategy that may be implemented after the consummation of the merger, including cost synergies realized, or to any additional costs incurred.

44

Table of Contents

Certain Projected Financial Information

The following is a summary of certain projected financial information that was included in each of the financial forecasts:

For purposes of the projected financial forecasts presented herein, (1) EBIT is calculated as net earnings before interest and taxes; (2) EBITDA is calculated as net earnings before interest, taxes, depreciation and amortization; and (3) unlevered free cash flow is calculated as EBITDA minus taxes, changes in net working capital and capital expenditures. Each of the foregoing calculations (i) excludes the projected results of operations from the Life Sciences business, the shared services related to the Life Sciences business and unusual and one-time items; and (ii) treats stock based compensation as a cash expense.

Important Information About Our Financial Forecasts

Our management believes that our financial forecasts were prepared in good faith and on a reasonable basis on the best information available to our management at the time of their preparation. Our financial forecasts, however, are not fact and should not be relied upon as necessarily indicative of actual future results, and actual results may differ materially from those contained in our financial forecasts.

The financial forecasts were not prepared with a view toward public disclosure, nor were they prepared with a view toward compliance with published guidelines of the SEC or U.S. GAAP. Neither the independent registered public accounting firm of AMTI nor any other independent accountants have compiled, examined, or performed any audit or other procedures with respect to the financial forecasts contained herein, nor have they expressed any opinion or any other form of assurance on such information or its achievability.

As noted above, our financial forecasts include assumptions as to certain business decisions that are subject to change, as well as assumptions related to industry performance and general economic conditions, each of which assumptions is inherently subjective and beyond the control of ATMI, including but not limited to expectations for demand and sales of new and existing products, customer and supplier relationships, research and development programs, market and technology opportunities, international trends, business strategies, business opportunities, objectives of management for future operations, microelectronics industry (including wafer start) growth and trends in the markets in which ATMI participates.

45

Table of Contents

By including our financial forecasts in this proxy statement, none of ATMI, Entegris or any of their respective representatives has made or makes any representation to any stockholder or to any other person regarding the ultimate performance of ATMI compared to the information contained in our financial forecasts. ATMI has made no representation to Entegris or Merger Sub, in the merger agreement or otherwise, concerning the probability of achieving the financial forecasts. Our financial forecasts summarized in this section were prepared during the periods described above and have not been updated to reflect any changes since the date they were made. We undertake no obligation, except as required by law, to update or otherwise revise our financial forecasts to reflect circumstances existing since their preparation or to reflect the occurrence of unanticipated events, even in the event that any or all of the underlying assumptions are shown to be in error, or to reflect changes in our business or general economic or industry conditions.

Effects on the Company if the Merger is Not Completed

If the merger agreement is not adopted by our stockholders or if the merger is not completed for any other reason, our stockholders will not receive any payment for their shares of ATMI common stock in connection with the merger. Instead, we will remain an independent public company, and ATMI common stock will continue to be quoted on the NASDAQ Global Select Market.

If the merger is not consummated, we expect that our management will operate the business in a manner similar to that in which it is being operated today and that our stockholders will be subject to the same risks and opportunities to which our business is currently subject, but there can be no assurance as to the effect of these risks and opportunities on the future value of your shares of ATMI common stock. In the event the merger is not completed, our board of directors will continue to evaluate and review our business operations, projects and capitalization, make such changes as are deemed appropriate and seek to identify acquisitions, joint ventures or strategic alternatives to enhance stockholder value. If the merger agreement is not adopted by our stockholders or if the merger is not consummated for any other reason, there can be no assurance that any other transaction acceptable to us will be offered or that our business, prospects or results of operations will not be adversely impacted.

If the merger agreement is terminated under certain circumstances, we may be obligated to pay Entegris a termination fee. Entegris may also be required to pay ATMI a termination fee under certain circumstances. See the section of this proxy statement entitled “The Merger Agreement — Termination Fees and Reimbursement of Expenses.”

Financing of the Merger

The obligations of ATMI under the merger agreement are not subject to a condition regarding Entegris’s or Merger Sub’s obtaining funds to consummate the merger and the other transactions contemplated by the merger agreement. Entegris has represented in the merger agreement that it will have available to it at the closing of the merger, sufficient cash to consummate the merger and to pay the aggregate merger consideration and any other amounts required to be paid by it in connection with the consummation of the transactions contemplated by the merger agreement and to pay all related fees and expenses of Entegris and Merger Sub, and that there is no restriction on the use of such cash for such purposes. Entegris has also represented in the merger agreement that it has delivered to the Company a true and complete copy of each of (i) a commitment letter, dated as of February 4, 2014, by and between Entegris and Goldman Sachs and (ii) a fee letter (with fees, economic terms and other customary provisions redacted), dated as of February 4, 2014, by and between Entegris and Goldman Sachs, pursuant to which Goldman Sachs has agreed to provide certain financing to Entegris in connection with the consummation of the merger.

The financing is anticipated to be comprised of the following sources:

46

Table of Contents

Material U.S. Federal Income Tax Consequences

The following is a general summary of material U.S. federal income tax consequences of the merger to U.S. holders whose shares of ATMI common stock are converted into the right to receive cash in the merger. This summary does not purport to consider all aspects of U.S. federal income taxation that might be relevant to our stockholders. For purposes of this summary, the term “U.S. holder” means a beneficial owner of shares of ATMI common stock that is, for U.S. federal income tax purposes:

A “non-U.S. holder” is a beneficial owner (other than a partnership or any entity or arrangement treated as a partnership for U.S. federal income tax purposes) of ATMI common stock that is not a U.S. holder. If a partnership (including an entity treated as a partnership for U.S. federal income tax purposes) holds ATMI common stock, the tax treatment of a partner generally will depend on the status of the partners and the activities of the partnership. A partner of a partnership (including an entity treated as a partnership for U.S. federal income tax purposes) holding ATMI common stock should consult its independent tax advisor.

This summary is based on the Internal Revenue Code of 1986, as amended (referred to in this proxy statement as the Code), its legislative history, U.S. Treasury regulations promulgated thereunder, published rulings by the Internal Revenue Service, and judicial and administrative decisions in effect as of the date of this proxy statement, all of which are subject to differing interpretations and to change, possibly with retroactive effect. This summary applies only to beneficial owners who hold shares of ATMI common stock as “capital assets” within the meaning of Section 1221 of the Code and does not apply to shares of ATMI common stock received in connection with the cancellation or exercise of employee stock options, restricted stock awards, restricted stock unit awards or Stock Credits under the Director Deferred Compensation Plans or otherwise as compensation for services or through a tax-qualified retirement plan, stockholders who hold an equity interest, directly or indirectly, in Entegris after the merger, or to certain types of beneficial owners who may be subject to special rules (such as insurance companies, banks, tax-exempt organizations, financial institutions, broker dealers, dealers in currencies, partnerships, S corporations or other pass-through entities (or investors in an S corporation or other pass-through entity), mutual funds, real estate investment trusts, controlled foreign corporations, passive foreign investment companies, traders in securities who elect the mark-to-market method of accounting for their securities, U.S. expatriates, stockholders subject to the alternative minimum tax, stockholders that have a functional currency other than the U.S. dollar, or stockholders who hold ATMI common stock as part of a hedge, straddle, constructive sale, conversion transaction or other integrated transaction). This summary does not address any aspect of state, local, foreign or federal non-income tax laws.

47

Table of Contents

U.S. Holders

Exchange of Shares of ATMI Common Stock for Cash Pursuant to the Merger Agreement. The receipt of cash in exchange for shares of ATMI common stock pursuant to the merger will be a taxable transaction for U.S. federal income tax purposes. In general, a U.S. holder whose shares of ATMI common stock are converted into the right to receive cash in the merger will recognize capital gain or loss for U.S. federal income tax purposes equal to the difference, if any, between the amount of cash received in the merger with respect to such shares and the holder’s adjusted tax basis in such shares. Gain or loss will be determined separately for each block of shares (i.e., shares acquired at the same cost in a single transaction). Such gain or loss will be long-term capital gain or loss, provided that a U.S. holder’s holding period is more than one year at the time of the consummation of the merger. Certain limitations apply to the use of capital losses. Long-term capital gains for certain non-corporate U.S. holders, including individuals, are generally eligible for a reduced rate of federal income taxation. In addition, certain non-corporate U.S. holders, including individuals, may be subject to an additional 3.8% tax on all or a portion of their “net investment income,” which may include all or a portion of the gain recognized in connection with the merger.

Backup Withholding and Information Reporting. The receipt of cash in exchange for shares of ATMI common stock by a U.S. holder pursuant to the merger may be subject to information reporting and backup withholding tax at the applicable rate, unless the U.S. holder (i) timely furnishes an accurate taxpayer identification number and otherwise complies with applicable U.S. information reporting or certification requirements (typically by completing and signing an Internal Revenue Service Form W-9, a copy of which will be included as part of the letter of transmittal to be timely returned to the paying agent); or (ii) is a corporation or other exempt recipient and, when required, establishes such fact in a manner satisfactory to the paying agent. U.S. holders who are exempt recipients not subject to backup withholding should indicate their exempt status on the Internal Revenue Service Form W-9 included as part of the letter of transmittal to be timely returned to the paying agent. Backup withholding is not an additional tax and any amounts withheld under the backup withholding rules may be refunded or credited against a U.S. holder’s U.S. federal income tax liability, if any, provided that the required information is furnished to the Internal Revenue Service in a timely manner.

Appraisal Rights. Generally, a U.S. holder of ATMI common stock who properly demands and perfects appraisal rights under Delaware law with respect to such holder’s ATMI common stock will recognize capital gain or loss for U.S. federal income tax purposes equal to the difference, if any, between the amount of cash received in respect to such shares and the holder’s adjusted tax basis in such shares, except that a portion of the cash received may be taxable as interest.

Non-U.S. Holders

Exchange of Shares of ATMI Common Stock for Cash Pursuant to the Merger Agreement. Any gain realized on the receipt of cash in the merger by a non-U.S. holder generally will not be subject to U.S. federal income tax unless:

48

Table of Contents

Backup Withholding and Information Reporting. A non-U.S. holder will be subject to information reporting and, in certain circumstances, backup withholding with respect to the cash received by such holder pursuant to the merger, unless such non-U.S. holder certifies under penalties of perjury that it is not a United States person (and the payor does not have actual knowledge or reason to know that the holder is a “United States person” as defined under the Code) or such holder otherwise establishes an exemption from backup withholding. Backup withholding is not an additional tax and any amounts withheld under the backup withholding rules may be refunded or credited against a non-U.S. holder’s U.S. federal income tax liability, if any. In order to avoid backup withholding, a non-U.S. holder should complete and sign an appropriate Form W-8 which may be obtained at www.irs.gov.

The U.S. federal income tax consequences described above are not intended to constitute tax advice nor a complete discussion of all tax consequences relating to the merger. Because individual circumstances may differ, each stockholder should consult its independent tax advisor regarding the applicability of the rules discussed above and the particular tax effects to the stockholder of the merger in light of such stockholder’s particular circumstances, the application of state, local, foreign and federal non-income tax laws, and, if applicable, the tax consequences of the receipt of cash in connection with the cancellation or exchange of options, restricted stock awards, restricted stock unit awards or Stock Credits under the Director Deferred Compensation Plans, including the transactions described in this proxy statement relating to our other equity compensation and benefit plans.

Interests of Certain Persons in the Merger

When considering the recommendation by our board of directors that our stockholders adopt the merger agreement, you should be aware that our directors and executive officers may have interests in the merger that are different from, or in addition to, the interests of our other stockholders. Our board of directors was aware of these interests and considered them, among other matters, in unanimously approving and declaring advisable the execution, delivery and performance of the merger agreement and the transactions contemplated by the merger agreement, including the merger, and determining that entering into the merger agreement and consummating the merger, are fair to, and in the best interests of, ATMI’s stockholders, and in making its recommendation that ATMI’s stockholders adopt the merger agreement. These interests are described below.

Beneficial Ownership and Treatment of ATMI Common Stock

As of March 10, 2014, the record date for the special meeting, our directors and executive officers beneficially owned and were entitled to vote, in the aggregate, approximately 1,644,200 shares of ATMI common stock, or approximately 4.84% of the total ATMI common stock outstanding on that date. These numbers do not give effect to outstanding stock options, Restricted Stock Unit Awards or Stock Credits under the Director Deferred Compensation Plans (as defined below), which are not entitled to vote at the special meeting, but do include Restricted Stock Awards which are entitled to vote at the special meeting.

Our directors and executive officers will receive the same $34.00 per share for their outstanding shares of ATMI common stock as our other stockholders. For further information with respect to the ownership of ATMI common stock of our directors and executive officers, see “Security Ownership of Certain Beneficial Owners, Directors and Executive Officers.”

49

Table of Contents

Treatment of Outstanding Equity Awards, Director Deferred Compensation Plans and Employee Stock Purchase Plan

Stock Options

The merger agreement provides that, immediately prior to the effective time of the merger, each option to acquire shares of ATMI common stock that is then outstanding and that has an exercise price less than the $34.00 per share merger consideration, whether or not then vested or exercisable, will be cancelled and terminated, and each holder of such an option will have the right to receive an amount of cash equal to (i) the number of shares of ATMI common stock subject to each such option, multiplied by (ii) the excess of $34.00 over the exercise price per share of each such option, less any applicable withholding taxes.

Restricted Stock Awards

The merger agreement provides that, immediately prior to the effective time of the merger, each Company Restricted Stock Award that is then outstanding will be cancelled and terminated, and each holder of a Company Restricted Stock Award will have the right to receive an amount in cash equal to (i) the number of shares of ATMI common stock subject to such Company Restricted Stock Award, multiplied by (ii) $34.00, less any applicable withholding taxes.

Restricted Stock Unit Awards

The merger agreement provides that, immediately prior to the effective time of the merger, each Company Restricted Stock Unit Award that is then outstanding will be cancelled and terminated, and each holder of a Company Restricted Stock Unit Award will have the right to receive an amount in cash equal to (i) the number of shares of ATMI common stock subject to such Company Restricted Stock Unit Award (determined based on the actual performance achieved as if the closing date of the merger represented the end date of the performance period), multiplied by (ii) $34.00, less any applicable withholding taxes.

Director Deferred Compensation Plan

The merger agreement provides that following the consummation of the merger, each non-employee director who is a participant in a Director Deferred Compensation Plan will have the right to receive, upon their termination of service on our board, an amount in cash equal to the product of (i) the number of Stock Credits (as defined in the applicable Director Deferred Compensation Plan) credited to such participant’s Stock Account (as defined in the applicable Director Deferred Compensation Plan), multiplied by (ii) $34.00 less any applicable withholding taxes.

Employee Stock Purchase Plan

The merger agreement provides that as soon as practicable following the date of the merger agreement, ATMI will take all actions necessary (i) to suspend the ATMI 1998 Employee Stock Purchase Plan (referred to in this proxy statement as the ESPP) effective immediately such that no additional offering periods shall be commenced between the date of the merger agreement and the effective time of the merger, (ii) to cancel each outstanding right to purchase shares of ATMI common stock in accordance with the ESPP and (iii) to refund all sums collected from participants during the offering period (as defined in the ESPP) then in progress.

Summary Table

The following table shows, for each executive officer and each director, as applicable, (i) the number of shares of ATMI common stock subject to vested and unvested options held by him or her; (ii) the cash consideration that he or she will receive for such options upon completion of the merger; (iii) the number of shares of ATMI common stock subject to unvested Company Restricted Stock Awards held by him or her; (iv) the cash consideration that he or she will receive for such Company Restricted Stock Awards upon completion of the merger; (v) the number of shares of ATMI common stock subject to Company Restricted Stock Unit Awards (determined based on achievement of the maximum level of performance under such awards) held

by him or her; (vi) the cash consideration that he or she will receive for such Company Restricted Stock Unit

50

Table of Contents

Awards upon completion of the merger; (vii) the number of Stock Credits credited to his or her Stock Account under the applicable Director Deferred Compensation Plan; (viii) the cash consideration that he or she will receive for such Stock Credits following completion of the merger in accordance with the terms of the applicable Director Deferred Compensation Plan; and (ix) the total cash consideration he or she will receive for all outstanding equity awards upon completion of the merger, and for all Stock Credits following completion of the merger in accordance with the terms of the applicable Director Deferred Compensation Plan, in each case as of an assumed merger closing date of April 30, 2014, based on applicable holdings on the date hereof and assuming continued employment or service through the assumed merger closing date (and as such without regard to any grants that may be made after the date hereof).

Employment Agreements

ATMI is a party to employment agreements with Douglas A. Neugold, Chairman, President and Chief Executive Officer, Daniel P. Sharkey, Executive Vice President, Business Development, and Timothy C. Carlson, Executive Vice President, Chief Financial Officer and Treasurer, as amended through February 3, 2014 (the employment agreements collectively, as amended, referred to in this proxy statement as the Employment Agreements).

51

Table of Contents

Pursuant to the Employment Agreements, if ATMI terminates an executive without “cause”, or if an executive resigns for “good reason”, within 548 days following a “change in control” (in each case as defined the Employment Agreements), which would include the merger, ATMI will pay the executive cash severance equal to two and a half (2.5) times the sum of the executive’s then-current annual base salary and annual target bonus, for a period of thirty (30) months after termination (with respect to Mr. Neugold), or cash severance equal to two (2) times the sum of the executive’s then-current annual base salary and annual target bonus for a period of twenty-four (24) months after termination (in the case of Messrs. Sharkey and Carlson). In addition, the Employment Agreements provide that, (i) with respect to Company Restricted Stock Unit Awards, the executive would be entitled to acceleration of the end of the performance period to the date of the change of control, and vesting would then be determined as of such date (and any applicable time vesting would remain in place following the change of control), (ii) with respect to Company Restricted Stock Awards, the executive would be entitled to accelerated vesting of such awards and (iii) all options to acquire shares of ATMI common stock held by the executives would vest and would remain exercisable for one year following termination (or until expiration of the options, if sooner). In addition, if the executive elects continued health care and/or dental coverage under the Consolidated Omnibus Budget Reconciliation Act of 1985 (referred to in this proxy statement as COBRA), ATMI would contribute to the cost of such coverage on the same basis ATMI would have contributed to the cost of such coverage had the executive continued to be an active ATMI employee, and the executive will be eligible to receive outplacement services selected by ATMI and at ATMI’s expense for six months following termination.

As a condition of an executive’s receipt of the severance payments and benefits under the Employment Agreements, the executive is required to execute, and not revoke, a release of claims, and will be subject to certain non-competition and non-solicitation restrictions (for two (2) years in the case of Mr. Neugold, and one (1) year for Messrs. Sharkey and Carlson).

Under the Employment Agreements, if an amount payable to the employee constitutes a “parachute payment” within the meaning of Section 280G of the Code, such payment will be reduced to the extent necessary so that no amount payable to the executive constitutes a “parachute payment.” However, the executive’s payments will not be subject to reduction if the net after-tax payment to which the executive would otherwise be entitled without such reduction would be greater than the net after-tax payment to the executive resulting from the receipt of such payments with such reduction. All determinations under the provision will be made by a nationally recognized accounting firm mutually agreed to by the employee and ATMI.

See “Proposal 3: Advisory Vote Regarding Golden Parachute Compensation” for quantification of the severance payments and benefits to which Messrs. Neugold, Sharkey and Carlson would be entitled under their employment agreements upon a qualifying termination of employment.

Executive Severance Pay Plan

On February 3, 2014, ATMI announced the ATMI, Inc. Executive Severance Pay Plan (referred to in this proxy statement as the Severance Plan). The Severance Plan, which becomes effective as of the date of a “change of control” (as defined in the Severance Plan), which would include the merger, provides severance protection for eligible employees in the event of termination of employment under certain circumstances in connection with the change of control.

The following executive officers are eligible to participate in the Severance Plan: Lawrence H. Dubois, Senior Vice President and Chief Technology Officer, Christian F. Kramer, Senior Vice President and General Manager, Microelectronics, Kathleen G. Mincieli, Senior Vice President, Human Resources and Patrick J. Shima, Senior Vice President and Chief Legal Officer.

In order to participate in the Severance Plan, each eligible executive will enter into a restrictive covenants agreement with ATMI that provides that, for a period of twelve (12) months following termination of the

52

Table of Contents

executive’s employment with ATMI, the executive will be subject to certain covenants regarding non-competition, non-solicitation of employees and non-interference with ATMI’s business.

Under the Severance Plan, upon termination of an eligible executive’s employment without “cause” or resignation for “good reason” (in each case as defined in the Severance Plan) within eighteen (18) months following a change of control, the executive would be entitled to severance pay equal to one and a half (1.5) times the sum of the executive’s then-current annual base salary and annual target bonus, for a period of eighteen (18) months after termination. In addition, if the executive elects continued health care coverage under COBRA, in lieu of otherwise applicable COBRA rates, the executive’s contributions will be at the then-applicable active employee rate, and the executive will be eligible to receive outplacement services selected by ATMI and at ATMI’s expense for six months.

As a condition of an executive’s receipt of the payments and benefits under the Severance Plan, the executives are required to execute, and not revoke, a release of claims.

Under the Severance Plan, if an amount payable to an executive constitutes a “parachute payment” within the meaning of Section 280G of the Code, such payment will be reduced to the extent necessary so that no amount payable to the executive constitutes a “parachute payment”. However, the executive’s payments will not be subject to reduction if the net after-tax payment to which the executive would otherwise be entitled without such reduction would be greater than the net after-tax payment to the executive resulting from the receipt of such payments with such reduction. All determinations under the provision will be made by a nationally recognized accounting firm mutually agreed to by the executive and ATMI.

See “Proposal 3: Advisory Vote Regarding Golden Parachute Compensation” for quantification of the severance payments and benefits to which Messrs. Kramer and Dubois would be entitled under the Severance Plan upon a qualifying termination of employment.

Assuming a merger closing date of April 30, 2014, and assuming that the employment of Ms. Mincieli and Mr. Shima is terminated without cause immediately following the closing on April 30, 2014, (i) the aggregate amount of cash severance payments under the Severance Plan would be $607,500 with respect to Ms. Mincieli and $709,125 with respect to Mr. Shima, and (ii) the value of continued medical and dental coverage and outplacement services, in each case under the Severance Plan, would be $22,191 with respect to Ms. Mincieli and $39,161 with respect to Mr. Shima. These amounts do not reflect any reductions which may be made to payments which constitute “parachute payments” under the Code.

Transaction Bonus Agreement

On January 13, 2014, ATMI entered into a transaction bonus agreement (referred to in this proxy statement as the Transaction Bonus Agreement) with Christian Kramer, as well as with certain other (non-executive officer) employees of the Company.

The Transaction Bonus Agreement generally provides that, upon a “change of control” (as defined in the Transaction Bonus Agreement), which includes the merger, within one (1) year following the effective date of the Transaction Bonus Agreement, subject to ATMI’s shareholders receiving “transaction value” (as defined in the Transaction Bonus Agreement) of at least $900,000,000, Mr. Kramer would be entitled to a transaction bonus equal to the sum of (i) the total transaction value, multiplied by the “base bonus ratio” (as defined in the Transaction Bonus Agreement) of 0.20%, multiplied by 17.5%, and (ii) the excess amount of transaction value above $1,000,000,000, multiplied by the “additional bonus ratio” (as defined in the Transaction Bonus Agreement), which ranges from 0% to 0.20% based on the amount of transaction value, multiplied by 17.5%. The transaction bonus will be paid in a cash lump sum within five days following the change of control.

In order to be eligible for a transaction bonus, Mr. Kramer generally must remain employed through the change of control. However, if Mr. Kramer’s employment is terminated without “cause” (as defined in the Transaction Bonus Agreement) following the signing of a definitive agreement in respect of a change of control, he will remain eligible for the transaction bonus if the change of control is consummated within one (1) year

53

Table of Contents

following the effective date of the Transaction Bonus Agreement, subject to Mr. Kramer’s continued compliance with restrictive covenants in any equity award agreement or other agreement between Mr. Kramer and ATMI.

Pursuant to the Transaction Bonus Agreement, if an amount payable to Mr. Kramer constitutes a “parachute payment” within the meaning of Section 280G of the Code, such payment will be reduced to the extent necessary so that no amount payable to the executive constitutes a “parachute payment.” However, Mr. Kramer’s payments will not be subject to reduction if the net after-tax payment to which he would otherwise be entitled without such reduction would be greater than the net after-tax payment to him resulting from the receipt of such payments with such reduction. All determinations under the provision will be made by a nationally recognized accounting firm designated by ATMI.

See “Proposal 3: Advisory Vote Regarding Golden Parachute Compensation” for quantification of the transaction bonus payment to which Mr. Kramer is entitled under the Transaction Bonus Agreement.

Cash Payments to Directors

On February 3, 2014, our board of directors approved payments of $100,000 to each of directors Mark A. Adley and Mark B. Segall for their efforts in connection with ATMI’s evaluation of strategic alternatives in their capacity as directors (including as members of the transaction committee), which amounts shall be paid to such individuals on or prior to completion of the merger.

Indemnification and Insurance

All rights to indemnification, advancement of expenses and exculpation from liabilities for acts or omissions occurring at or prior to the effective time of the merger existing in favor of the current or former directors, officers or employees of ATMI and its subsidiaries as provided in their respective certificates of incorporation or by-laws (or comparable organizational documents) and any indemnification or other similar agreements of ATMI or any of its subsidiaries, in each case as in effect on the date of the merger agreement, will continue in full force and effect in accordance with their terms. For six years following the effective time of the merger, the surviving company will, and Entegris will cause the surviving company to, maintain in effect the provisions in its certificate of incorporation and by-laws to the extent they provide for indemnification, advancement and reimbursement of expenses and exculpation of each ATMI indemnified party (as described below), with respect to facts or circumstances occurring at or prior to the effective time of the merger, on the same basis as set forth in the ATMI certificate of incorporation and ATMI by-laws in effect on the date of the merger agreement, to the fullest extent permitted from time to time under applicable law, which provisions shall not be amended except as required by applicable law or except to make changes permitted by applicable law that would enlarge the scope of the indemnified parties’ indemnification rights thereunder.

From and after the effective time of the merger, to the fullest extent permitted by applicable law (including to the fullest extent authorized or permitted by any amendments to or replacements of the DGCL adopted after the date of the merger agreement that increase the extent to which a corporation may indemnify its officers and directors) the surviving company will indemnify and hold harmless each individual who was as of the date of the merger agreement, or who becomes prior to the effective time of the merger, a director or officer of ATMI or any of its subsidiaries or who was as of the date of the merger agreement, or who thereafter commences prior to the effective time of the merger, serving at the request of ATMI or any of its subsidiaries as a director or officer of another entity, against all losses incurred in connection with any actual or threatened legal action arising out of or pertaining to the fact that such person is or was an officer or director of ATMI or any of its subsidiaries or is or was serving at the request of ATMI or any of its subsidiaries as a director or officer of another entity, whether asserted or claimed prior to, at or after the effective time of the merger. In the event of any such legal action, each such person will be entitled to advancement of expenses incurred in the defense of any such legal action from the surviving company within ten business days of receipt by the surviving company from such person of a request therefor; provided, that any person to whom expenses are advanced provides an undertaking, if and only

54

Table of Contents

to the extent required by the DGCL or the surviving company’s certificate of incorporation or by-laws, to repay such advances if it is ultimately determined by final adjudication that such person is not entitled to indemnification. The surviving company will cooperate in the defense of any such matter.

For a period of six years after the effective time of the merger, the surviving company must either cause to be maintained in effect the current policies of directors’ and officers’ liability insurance and fiduciary liability insurance maintained by ATMI or its subsidiaries or provide substitute policies for ATMI and its current and former directors and officers who are currently covered by the directors’ and officers’ and fiduciary liability insurance coverage currently maintained by ATMI in either case, of not less than the existing coverage and having other terms not less favorable to the insured persons than the directors’ and officers’ liability insurance and fiduciary liability insurance coverage currently maintained by ATMI with respect to claims arising from facts or events that occurred on or before the effective time of the merger, except that the surviving company will not be required to pay for any one policy year of such insurance policies, more than 300% of the aggregate annual premium most recently paid by ATMI prior to the date of the merger agreement, and if the surviving company is unable to obtain such insurance it must obtain as much comparable insurance as possible for the years within such six-year period for an annual premium equal to such maximum amount, in respect of each policy year within such period. In lieu of such insurance, prior to the closing date of the merger ATMI may, at its option (following reasonable consultation with Entegris), purchase a “tail” directors’ and officers’ liability insurance policy and fiduciary liability insurance policy for ATMI and its current and former directors and officers who are currently covered by the directors’ and officers’ and fiduciary liability insurance coverage maintained by ATMI as of the date of the merger agreement, with such tail policy providing coverage in an amount not less than the existing coverage and having other terms not less favorable to the insured persons than the directors’ and officers’ liability insurance and fiduciary liability insurance coverage maintained by ATMI as of the date of the merger agreement with respect to claims arising from facts or events that occurred on or before the effective time of the merger. However, in no event may the cost of any such tail policy in respect of any one policy year exceed 300% of the aggregate annual premium most recently paid by ATMI prior to the date of the merger agreement in respect of its directors’ and officers’ liability insurance and fiduciary liability insurance policies.

Governmental and Regulatory Approvals

Under the HSR Act, and the rules promulgated thereunder by the FTC, the merger may not be completed until notification and report forms have been filed with the FTC and the Antitrust Division of the DOJ, and the applicable waiting period has expired or been terminated. ATMI and Entegris filed the notification and report forms under the HSR Act with the FTC and the DOJ on February 19, 2014, which triggered an initial 30-day waiting period. The DOJ, the FTC, state Attorneys General or private parties may also challenge the merger on antitrust grounds either before or after the transaction has closed. Accordingly, while the parties believe that the transaction complies with the applicable antitrust laws, it is possible that at any time before or after expiration or termination of the HSR Act waiting period or even after the completion of the merger, any of the DOJ, the FTC, state Attorneys General or private parties could take action under the antitrust laws as deemed necessary or desirable in the public or other interest, including without limitation seeking to enjoin the completion of the merger or permitting completion subject to regulatory concessions or conditions.

At any time before or after consummation of the merger, notwithstanding expiration or early termination of the waiting period under the HSR Act, the DOJ or the FTC could take such action under the antitrust laws as it deems necessary or desirable in the public interest, including seeking to enjoin the consummation of the merger or seeking divestiture of substantial assets of ATMI or Entegris. At any time before or after the consummation of the merger, and notwithstanding the expiration or early termination of the waiting period under the HSR Act, any state could take such action under the antitrust laws as it deems necessary or desirable in the public interest. Such action could include seeking to enjoin the consummation of the merger or seeking divestiture of substantial assets of ATMI or Entegris. Nothing in the merger agreement will (i) require Entegris or Merger Sub to sell, divest, convey or hold separate or otherwise take any other action (and ATMI will not undertake any such action without Entegris’s prior written consent) that limits Entegris’s and its subsidiaries’ freedom of action with respect to, or

55

Table of Contents

their ability to retain, particular products, assets or businesses of Entegris or ATMI or their respective subsidiaries, or agree to take any such action, other than, solely in respect of products, assets or businesses of ATMI (and not any products, assets, or businesses of Entegris), only to the extent that such action would not reasonably be expected to impact in any material respect the expected benefits to Entegris and its subsidiaries, taken as a whole, of the transactions contemplated by the merger agreement; (ii) require Entegris, ATMI or their respective subsidiaries to take or agree to take any action with respect to its business or operations unless the effectiveness of such agreement or action is conditioned upon the closing of the merger; (iii) require any of the parties to the merger agreement to compensate any third party, commence or participate in litigation or offer or grant any accommodation (financial or otherwise) to any third party to obtain any such consent or approval; or (iv) permit ATMI or any of its subsidiaries to take or agree to certain other actions without Entegris’s prior written consent, not to be unreasonably withheld, with respect to (ii) above, in order to obtain antitrust clearance (see the section of this proxy statement entitled “The Merger Agreement — Regulatory Matters”). Private parties may also seek to take legal action under the antitrust laws under certain circumstances.

In addition to those approvals required pursuant to the HSR Act, and the rules promulgated thereunder, the parties have agreed to obtain certain other approvals under non-U.S. antitrust laws as a condition to the closing of the merger. Under the merger control rules of certain jurisdictions outside the United States where the parties conduct business, filings will be required and it may be necessary to observe waiting periods and/or obtain approvals prior to the completion of the merger. The period for review of the merger will vary from jurisdiction to jurisdiction and may be affected by a variety of factors.

The term “antitrust laws” means the Sherman Act, as amended, the Clayton Act, as amended, the HSR Act, the Federal Trade Commission Act, as amended, all applicable foreign antitrust laws and all other applicable laws issued by any government, court, regulatory or administrative agency, commission or authority or other governmental instrumentality, whether federal, state or local, domestic, foreign or multinational, designed or intended to prohibit, restrict or regulate actions having the purpose or effect of monopolization or restraint of trade or lessening of competition through merger or acquisition.

We cannot assure you that an antitrust or other regulatory challenge to the merger will not be made.

Delisting and Deregistration of ATMI Common Stock

If the merger is completed, ATMI common stock will no longer be traded on the NASDAQ Global Select Market and will be deregistered under the Exchange Act, and we will no longer be required to file periodic reports with the SEC in respect of ATMI common stock.

Litigation Related to the Merger

On or about February 7 and 28, 2014, two putative class action complaints challenging the merger were filed in the Superior Court of the State of Connecticut, Judicial District of Danbury, captioned Andrew Pace v. ATMI, Inc., et al. and Dolores Carter v. ATMI, Inc., et al., respectively. The complaints were filed on behalf of the public shareholders of ATMI and name as defendants ATMI, the members of its board of directors, Entegris and Merger Sub. The complaints generally allege that ATMI’s directors breached their fiduciary duties to ATMI’s shareholders by agreeing to sell ATMI for inadequate and unfair consideration and pursuant to an inadequate and unfair process, and that ATMI, Entegris and Merger Sub aided and abetted those alleged breaches. The complaint in the Carter action also alleges purported disclosure deficiencies in the preliminary proxy statement for the merger that ATMI filed with the SEC on February 25, 2014. The complaints seek, among other things, to enjoin the merger. The defendants have not yet responded to the complaints, but believe that the claims asserted against them are without merit.

56

Table of Contents

THE MERGER AGREEMENT

The following describes certain material provisions of the merger agreement, which is attached as Annex A to this proxy statement and which is incorporated by reference herein. The description in this section and elsewhere in this proxy statement is qualified in its entirety by reference to the merger agreement. This summary does not purport to be complete and may not contain all of the information about the merger agreement that is important to you. ATMI encourages you to read carefully the merger agreement in its entirety before making any decisions regarding the merger because it is the principal document governing the merger.

The merger agreement and this summary of its terms have been included to provide you with information regarding the terms of the merger agreement. Factual disclosures about ATMI contained in this proxy statement or in ATMI’s public reports filed with the SEC may supplement, update or modify the factual disclosures about ATMI contained in the merger agreement and described in this summary. The representations, warranties and covenants made in the merger agreement by ATMI were qualified and subject to important limitations agreed to by ATMI in connection with negotiating the terms of the merger agreement and may be subject to a contractual standard of materiality which may differ from what may be viewed as material by investors. In particular, in your review of the representations and warranties contained in the merger agreement and described in this summary, it is important to bear in mind that the representations and warranties were negotiated with the principal purposes of establishing the circumstances in which a party to the merger agreement may have the right not to close the merger if the representations and warranties of the other party prove to be untrue due to a change in circumstance or otherwise, and allocating risk between the parties to the merger agreement, rather than establishing matters as facts. Information concerning the subject matter of the representations and warranties, which do not purport to be accurate as of the date of this proxy statement, may have changed since the date of the merger agreement.

The Merger

Subject to the terms and conditions of the merger agreement and in accordance with the DGCL, at the effective time of the merger, Merger Sub, a wholly owned subsidiary of Entegris and a party to the merger agreement, will merge with and into ATMI. ATMI will survive the merger as a direct wholly owned subsidiary of Entegris (following the merger, ATMI is referred to in this proxy statement as the surviving company) and the separate corporate existence of Merger Sub will cease.

Effective Time; Closing

The effective time of the merger will occur at the time the parties file a certificate of merger with the Secretary of State of the State of Delaware on the closing date of the merger or such later time as agreed to by Entegris and ATMI and specified in the certificate of merger.

Unless ATMI and Entegris agree otherwise, the closing of the merger will occur on the second business day after the conditions to the merger set forth in the merger agreement have been satisfied or waived. However, if the “marketing period” (as described below) has not ended at the time of the satisfaction or waiver of such conditions (other than those conditions that by their nature are to be satisfied at the closing), the closing of the merger will take place instead on the earlier to occur of (i) any business day during the marketing period to be specified by Entegris to ATMI on no less than two business days’ written notice to ATMI and (ii) the third day following the final day of the marketing period, but in each case subject to the satisfaction or waiver of the conditions to the merger.

Marketing Period

The “marketing period” referred to above is the first period of 18 consecutive business days starting on the first business day after the date of ATMI’s delivery of the “required information” (as described under “— Financing Covenant”) throughout which (i) Entegris will have all of the required information regarding ATMI and during which period such information will remain compliant with applicable securities laws and

57

Table of Contents

(ii) the conditions to each party’s obligations to close the merger have been satisfied (other than those conditions that by their terms are to be satisfied at the closing of the merger) and nothing has occurred and no condition exists that would cause any of the closing conditions set forth in the merger agreement to fail to be satisfied, assuming that the closing date of the merger were to be scheduled for any time during such 18 consecutive business day period.

However, the marketing period will not commence if, prior to the completion of the marketing period, (i) ATMI’s auditors will have withdrawn or qualified any audit opinion with respect to the required information (in which case the marketing period will not be deemed to commence unless and until a new unqualified audit opinion is issued by ATMI’s independent accountants or former independent accountants (which will be an independent registered public accounting firm)), (ii) the financial statements included in the required information that are available to Entegris on the first day of the marketing period would not be sufficiently current on any day during such period to be compliant (in which case the marketing period will not be deemed to commence until the receipt by Entegris of updated required information that is compliant), (iii) ATMI issues a public statement indicating its intent to restate any material financial information of ATMI or that any such restatement is under consideration or may be a possibility (in which case the marketing period will not be deemed to commence unless and until such restatement has been completed and the relevant financial statements have been amended or ATMI has determined that no restatement will be required in accordance with GAAP) or (iv) ATMI will have failed to file any annual, quarterly or period report with the SEC that was required to be filed by it with the SEC by the date required under the Exchange Act containing all of the financial information required to be contained therein (in which case the marketing period will not be deemed to commence unless and until all such reports have been filed).

The marketing period will end on any earlier date on which the entire debt financing has been consummated in accordance with its terms.

Merger Consideration

ATMI Common Stock

The merger agreement provides that each share of ATMI common stock outstanding immediately prior to the effective time of the merger (other than shares of ATMI common stock owned by ATMI as treasury stock or owned directly by Entegris, Merger Sub, ATMI BVBA or any of its subsidiaries (referred to in this proxy statement as a Life Sciences subsidiary) or by any direct or indirect wholly-owned subsidiary of ATMI, Entegris or Merger Sub, Company Restricted Stock Awards or shares of ATMI common stock the holders of which have properly perfected their appraisal rights under Delaware law) will be cancelled and converted into the right to receive $34.00 in cash, without interest or dividends thereon, less any applicable withholding taxes.

The merger agreement provides that each share of ATMI common stock held by ATMI as treasury stock and each share of ATMI common stock owned by Entegris, Merger Sub or any Life Sciences subsidiary will be cancelled and no consideration will be delivered in exchange therefor. Shares of ATMI common stock owned by any direct or indirect wholly owned subsidiary of ATMI that is not a Life Sciences subsidiary (referred to in this proxy statement as a Non-Life Sciences subsidiary), any direct or indirect wholly owned subsidiary of Entegris (other than Merger Sub) or of Merger Sub will be converted into a number of shares of ATMI common stock of the surviving company so that the percentage ownership of such subsidiary of the surviving company immediately following the effective time of the merger will equal the ownership percentage of such subsidiary in ATMI immediately prior to the effective time of the merger. Shares of ATMI common stock held by a stockholder who has not voted in favor of the merger and is entitled to demand and has properly demanded his appraisal rights will not be converted into the right to receive the merger consideration. Such stockholder will instead be entitled to the appraisal rights provided under the DGCL as described under “Appraisal Rights.”

Each issued and outstanding share of capital stock of Merger Sub will be converted into and become one validly issued, fully paid and nonassessable share of ATMI common stock, par value $0.01, of the surviving company.

58

Table of Contents

Treatment of ATMI Stock Options, Restricted Stock Awards and Restricted Stock Unit Awards, ESPP and ATMI Stock Plans

ATMI Stock Options

Immediately prior to the effective time of the merger, each option to acquire shares of ATMI common stock that is then outstanding and that has an exercise price less than the merger consideration, whether or not then vested or exercisable, will be cancelled and terminated in exchange for the right to receive a cash amount (less applicable withholding taxes, if any) equal to (i) the number of shares of ATMI common stock subject to such option, multiplied by (ii) the excess of (1) the merger consideration over (2) the exercise price per share of such option, payable through payroll promptly following the closing date of the merger (but in any event no later than the later of ten business days following the closing date of the merger and the first regular payroll date following the closing date of the merger). With respect to any option that is outstanding immediately prior to the effective time of the merger that is not eligible for such cash payment, ATMI will cause the cancellation of such ATMI stock option without any payment or consideration therefor.

Company Restricted Stock Awards

Immediately prior to the effective time of the merger, each Company Restricted Stock Award that is then outstanding will be cancelled and terminated, and each holder of a such an award will have the right to receive from the surviving company, in respect of such award, an amount in cash (less applicable withholding taxes, if any) equal to (i) the number of shares of ATMI common stock subject to such award, multiplied by (ii) the merger consideration, payable through payroll promptly following the closing date of the merger (but in any event no later than the later of ten business days following the closing date of the merger and the first regular payroll date following the closing date of the merger).

Company Restricted Stock Unit Awards

Immediately prior to the effective time of the merger, each Company Restricted Stock Unit Award that is then outstanding will be cancelled and terminated, and each holder of such an award will have the right to receive from the surviving company, in respect of such award, an amount in cash (less applicable withholding taxes, if any) equal to (i) the number of shares of ATMI common stock subject to such award (determined in accordance with terms of the applicable award based on the actual performance achieved as if the closing date of the merger represented the end date of the performance period), multiplied by (ii) the merger consideration, payable through payroll promptly following the closing date of the merger (but in any event no later than the later of ten business days following the closing date of the merger and the first regular payroll date following the closing date of the merger).

Employee Stock Purchase Plan

As soon as practicable following the date of the merger agreement, ATMI will take all actions necessary (i) to suspend the ESPP effective immediately such that no additional offering periods shall be commenced between the date of the merger agreement and the effective time of the merger, (ii) to cancel each outstanding right to purchase shares of ATMI common stock in accordance with the ESPP and (iii) to refund all sums collected from participants during the offering period (as defined in the ESPP) then in progress.

ATMI Stock Plans

Prior to the effective time of the merger, ATMI will take all actions (including obtaining any necessary determinations and/or resolutions of the ATMI board of directors or a committee thereof, which Entegris will have a reasonable opportunity to review and comment upon prior to their presentation to the ATMI board of directors or such committee) that may be necessary (under the ATMI stock plans and/or related award agreements and the ESPP) to terminate the ATMI, Inc. 1995 Stock Plan, the ATMI, Inc. 1997 Stock Plan, the

59

Table of Contents

ATMI, Inc. 1998 Stock Plan, the ATMI, Inc. 2000 Stock Plan, the ATMI, Inc. 2003 Stock Plan, and the ATMI, Inc. 2010 Stock Plan (referred to in this proxy statement as the ATMI stock plans) and the ESPP as of the effective time of the merger. As of the effective time of the merger, the ATMI stock plans and the ESPP shall be terminated and shall cease to exist without any liability to ATMI, Entegris, the surviving company or any of their respective subsidiaries (other than the obligation to pay the amounts otherwise set forth in the merger agreement).

ATMI Director Deferred Compensation Plan Stock Credits

Following the effective time of the merger, each participant in the Director Deferred Compensation Plans will have the right to receive from the surviving company an amount in cash (less applicable withholding taxes, if any) equal to the product of (i) the merger consideration, multiplied by (ii) the number of Stock Credits (as defined in the applicable Director Deferred Compensation Plan) then credited to such participant’s stock account (as defined in the applicable Director Deferred Compensation Plan), payable in accordance with the terms of the applicable Director Deferred Compensation Plan.

Withholding

ATMI, Entegris, the surviving company, the paying agent or other applicable withholding agent will be entitled to deduct and withhold from the consideration otherwise payable pursuant to the merger agreement such amounts as are required to be deducted and withheld with respect to the making of any such payment under applicable tax law. Amounts withheld and timely paid to the appropriate governmental entity will be treated for purposes of the merger agreement as having been paid to the person in respect of which such deduction or withholding was made.

Unexchanged Shares

No cash payment with respect to the merger consideration will be paid to the holder of any unsurrendered certificate (or shares of ATMI common stock held in book entry form) until the surrender of such certificate (or shares of ATMI common stock held in book entry form).

Conditions to the Completion of the Merger

The obligations of Entegris, Merger Sub and ATMI to effect the merger are subject to the satisfaction or waiver of the following conditions:

In addition, Entegris’s and Merger Sub’s obligations to effect the merger are subject to the following additional conditions:

60

Table of Contents

In addition, ATMI’s obligations to effect the merger are subject to the following additional conditions:

The closing of the Life Sciences transaction occurred on February 20, 2014, and as such, the closing conditions related to the Life Sciences transaction have been satisfied.

For purposes of the merger agreement, “material adverse effect” means, with respect to ATMI, any effect, change, event, circumstance or occurrence that, individually or in the aggregate, has had or would reasonably be expected to have a material adverse effect on (a) the business, results of operations, assets, liabilities or condition (financial or otherwise) of ATMI and the Non-Life Sciences subsidiaries, taken as a whole or (b) the ability of ATMI to consummate the merger or the other transactions contemplated in the merger agreement (including the sale of the Life Sciences business pursuant to the Life Sciences SAPA); provided, however, that none of the following, and no effect, change, event, circumstance or occurrence arising out of, or resulting from, the following, will constitute or be taken into account, individually or in the aggregate, in determining whether an ATMI material adverse effect has occurred or may occur: (A) changes generally affecting the economy, credit or financial or capital markets, in the United States or elsewhere in the world, including changes in interest or exchange rates; (B) changes generally affecting the industries in which ATMI and its subsidiaries operate; (C) changes or prospective changes in applicable law or GAAP or in accounting standards, any changes or

61

Table of Contents

prospective changes in the interpretation or enforcement of any of the foregoing or any changes in general legal, regulatory or political conditions, in each case occurring after the date hereof; (D) changes solely attributable to the announcement or pendency of the merger agreement, including the impact thereof on relationships, contractual or otherwise, with customers, suppliers, distributors, partners, employees or governmental entities, or any litigation arising from allegations of breach of fiduciary duty or violation of applicable law relating to the merger agreement or the transactions contemplated thereby to the extent addressed in the merger agreement; (E) acts of war (whether or not declared), sabotage or terrorism, or any escalation or worsening of any such acts of war (whether or not declared), sabotage or terrorism; (F) volcanoes, tsunamis, pandemics, earthquakes, floods, storms, hurricanes, tornados or other natural disasters; (G) any action taken by ATMI or its subsidiaries that is specifically required by the merger agreement or with the prior written consent or at the direction of Entegris in accordance with the merger agreement, or the failure to take any action by ATMI or its subsidiaries if that action is prohibited by the merger agreement; (H) changes resulting or arising from the identity of, or any facts or circumstances relating to the Entegris or any of its affiliates; (I) changes in the price or trading volume of ATMI common stock; or (J) any failure to meet any internal or public projections, forecasts, guidance, estimates, milestones, budgets or internal or published financial or operating predictions of revenue, earnings, cash flow or cash position (it being understood that the exceptions in clauses (I) and (J) shall not prevent or otherwise affect a determination that the underlying cause of any such change or failure referred to therein (to the extent not otherwise falling within any of the exceptions provided by clauses (A) through (H) hereof) is, may be, contributed to or may contribute to, an ATMI material adverse effect; provided further, however, that any effect, change, event or occurrence referred to in clauses (A), (B), (C), (E) or (F) above may be taken into account in determining whether or not there has been or may be an ATMI material adverse effect to the extent such effect, change, event, circumstance or occurrence has a material disproportionate adverse effect on ATMI and the Non-Life Sciences subsidiaries, taken as a whole, as compared to other participants in the industries in which ATMI and its subsidiaries operate. The determination of an ATMI material adverse effect shall in all events not take into account all effects, changes, events, circumstances or occurrences with respect to the Life Sciences business or any Life Sciences assets or liabilities to be transferred or assumed pursuant to the Life Sciences SAPA except to the extent, and only to the extent, that ATMI or any Non-Life Sciences subsidiary retains any liability or obligation, whether direct, indirect, contingent or otherwise, in respect thereof.

For purposes of the merger agreement, “material adverse effect” means, with respect to Entegris, any event, change, circumstance or occurrence that, individually or in the aggregate, would prevent or materially delay or adversely impact the ability of Entegris or Merger Sub to consummate the merger.

ATMI Stockholders Meeting

ATMI has agreed to call a meeting of its stockholders for the purpose of adopting the merger agreement, as soon as reasonably practicable after the SEC confirms that it has no further comments on this proxy statement. Unless the ATMI board of directors has effected an adverse recommendation change (as described in “— Non-Solicitation of Alternative Proposals” below) and otherwise subject to its fiduciary obligations, ATMI must use its reasonable best efforts, including engaging a proxy solicitation firm reasonably acceptable to Entegris to assist with proxy solicitations, to obtain adoption of the merger agreement by ATMI’s stockholders. ATMI may not adjourn, recess or postpone the special meeting except (i) to the extent necessary to ensure that any supplement or amendment to this proxy statement required by applicable law is provided to the stockholders of ATMI within a reasonable amount of time in advance of the ATMI stockholders meeting or (ii) if, as of the time for which the ATMI stockholders meeting is originally scheduled (as set forth in this proxy statement), there are insufficient shares of ATMI common stock represented (either in person or by proxy) to constitute a quorum necessary to conduct the business of the ATMI stockholders meeting or to solicit additional proxies and votes in favor of adoption of the merger agreement if sufficient votes to constitute stockholder approval has not been obtained.

Unless the merger agreement is terminated in accordance with its terms, ATMI’s obligations to hold the ATMI stockholders meeting will not be affected by the commencement, public proposal, public disclosure or communication to ATMI of any acquisition proposal or by the making of any adverse recommendation change by the ATMI board of directors (each as described below under “— Non-Solicitation of Alternative Proposals”).

62

Table of Contents

Non-Solicitation of Alternative Proposals

The merger agreement contains detailed provisions prohibiting ATMI from seeking an alternative transaction to the merger. Under these “no solicitation” provisions, ATMI has agreed that, from the date of the merger agreement until the earlier of the effective time of the merger or the termination of the merger agreement in accordance with its terms, ATMI shall not and shall cause its subsidiaries not to, and shall use its reasonable best efforts to cause its and its subsidiaries’ respective directors, officers, employees, accountants, consultants, legal counsel, financial advisors and agents and other representatives not to, directly or indirectly:

The merger agreement requires ATMI to, and to cause its subsidiaries and its and their directors and officers, and use its reasonable best efforts to cause its and their respective representatives (other than its and their directors and officers) to, immediately cease and terminate all discussions and negotiations with any person that may have been ongoing with respect to any acquisition proposal as of the date of the merger agreement. ATMI also agreed to request the prompt (but in no event later than 48 hours following the date of the merger agreement) return or destruction of all confidential information previously furnished to any person that has executed a confidentiality agreement with ATMI with respect to consideration of a possible acquisition proposal at any time after January 1, 2013 (other than agreements that have expired by their terms).

The merger agreement also provides that if, at any time prior to the adoption of the merger agreement by ATMI’s stockholders, ATMI or any of its representatives receives a bona fide written acquisition proposal which did not result from a breach of the non-solicitation provisions of the merger agreement, ATMI and its representatives are permitted to contact the person or group of persons who made the acquisition proposal to clarify terms for the sole purpose of ATMI’s board of directors informing itself about such acquisition proposal. In the event that ATMI’s board of directors determines in good faith, after consultation with its financial advisor and outside legal counsel, that such bona fide written acquisition proposal constitutes or would reasonably be expected to lead to a “superior proposal” (as described below) and that failure to take such action would be inconsistent with the directors’ fiduciary duties under applicable law, then ATMI is also permitted to:

63

Table of Contents

ATMI has also agreed in the merger agreement that it will promptly (and in no event later than 24 hours after receipt) notify Entegris orally and in writing after receipt by ATMI or any of its representatives of any acquisition proposal or request for non-public information relating to ATMI or any of its subsidiaries. Such prompt notice will include the identity of the person making the acquisition proposal or other request and the material terms and conditions thereof, and ATMI will further promptly (and in no event later than 24 hours after receipt) provide copies to Entegris of any written proposals, indications of interest, and/or draft agreements relating to such acquisition proposal. In addition, ATMI has agreed to keep Entegris informed on a prompt basis as to the status of any such acquisition proposal (including changes to any material terms thereof or any material developments with respect thereto) including by promptly (and in no event later than 24 hours after receipt) providing to Entegris copies of any additional or revised written proposals, indications of interest and/or draft agreements relating to such acquisition proposal.

For purposes of the merger agreement, the term “acquisition proposal” means any proposal or offer from any person or group of persons (other than Entegris or Merger Sub) providing for:

For purposes of the merger agreement, “superior proposal” means any unsolicited bona fide written acquisition proposal (with all references to “20%” in the definition of acquisition proposal being deemed to be references to “50%”) which the ATMI board of directors (or any committee thereof) determines in good faith (after consultation with its financial advisor and outside legal counsel and after taking into account all financial, legal, regulatory, timing and other aspects of such acquisition proposal and of the merger agreement (including any changes to the terms of the merger agreement proposed by Entegris, any fees to be paid by ATMI pursuant to the terms of the merger agreement and to the likelihood of consummating such acquisition proposal without undue delay in accordance with its terms):

64

Table of Contents

Change of Recommendation

The merger agreement provides that the ATMI board of directors will not effect an adverse recommendation change except in the limited circumstances described below. For purposes of the merger agreement, an “adverse recommendation change” would occur if the ATMI board of directors were to do any of the following:

At any time prior to the ATMI stockholders meeting, the ATMI board of directors may (i) effect an adverse recommendation change in response to an “intervening event” (as described below), if, and only if, the ATMI board of directors determines in good faith (after consultation with outside legal counsel) that failure to take such action would be inconsistent with the directors’ fiduciary duties under applicable law and (ii) if ATMI receives an acquisition proposal that the ATMI board of directors determines in good faith constitutes a superior proposal — after consultation with its financial advisors and outside legal counsel — authorize, adopt or approve such superior proposal and cause or permit ATMI to enter into an alternative acquisition agreement with respect to such superior proposal, provided ATMI terminates the merger agreement pursuant to the terms thereof concurrently with entering into such alternative acquisition agreement and pays the applicable termination fee. In each case of (i) and (ii) of the foregoing sentence, ATMI may only take such actions if:

65

Table of Contents

ATMI is required to comply with the obligations described in the foregoing three bullet points with respect to each superior proposal it receives or any intervening event the ATMI board of directors identifies.

For purposes of the merger agreement, an “intervening event” means a material event, development or change in circumstances with respect to ATMI occurring or coming to the attention of ATMI’s board of directors after the date of the merger agreement and prior to obtaining ATMI stockholder approval for the merger, and which was not known, and could not reasonably be expected to have known or foreseen, by the ATMI board of directors as of or prior to the date of the merger agreement; provided, however, that in no event will (A) the receipt, existence or terms of an acquisition proposal, (B) any events, developments or change in circumstances of Entegris, (C) the status of the merger under the HSR Act or of any of the required antitrust approvals, (D) any announcements, approvals, issuances, or regulations of any governmental entity, constitute an intervening event, or (E) any matter relating to the foregoing or consequence of the foregoing, constitute an intervening event.

The merger agreement permits ATMI or its board of directors to comply with Rule 14d-9 and Rule 14e-2 under the Exchange Act with respect to an acquisition proposal or to make other disclosures to the stockholders of ATMI if the ATMI board of directors (after consultation with outside legal counsel) concludes that the failure to do so would be inconsistent with its fiduciary duties under applicable law, provided, that any adverse recommendation change may only be made in accordance with the merger agreement.

Financing Covenant

Entegris and Merger Sub have agreed to use their reasonable best efforts to take (or cause to be taken) all actions and use their reasonable best efforts to do, or cause to be done, all things necessary or advisable to arrange debt financing and to consummate the debt financing at the effective time of the merger, including using reasonable best efforts to:

66

Table of Contents

Entegris and Merger Sub may amend, restate, replace, supplement or otherwise modify, or waive any of its rights under, the debt commitment letter, or obtain alternative financing, provided that Entegris shall not, without the prior written consent of ATMI, (A) reduce the aggregate amount of the debt financing, (B) impose new or additional conditions precedent or contingencies to the debt financing as set forth in the debt commitment letter or otherwise amend, modify, or expand any conditions precedent to the funding of the debt financing (unless such conditions precedent or contingencies to the alternative financing would not reasonably be expected to (i) prevent or delay the closing of the merger, (ii) make the funding of the debt financing less likely to occur, or (iii) adversely affect the ability of Entegris or Merger Sub to consummate the transactions contemplated by the merger agreement or to enforce its respective rights against the other parties to the debt commitment letter or the definitive agreements with respect thereto), (C) except in certain circumstances, release or consent to the termination of the obligations of the lenders under the debt commitment letter (except for certain assignments and replacements contemplated by the debt commitment letter), (D) otherwise prevent or delay the closing of the merger or (E) reasonably be expected to adversely impact the ability of Entegris or Merger Sub to enforce its rights against the other parties to the debt commitment letter or the definitive agreements with respect thereto. Notwithstanding the foregoing, Entegris and Merger Sub may amend, restate, replace, supplement or otherwise modify the debt commitment letter (or any alternative financing) on one or more occasions to add additional arrangers, bookrunners, agents and lenders in accordance with the terms of the debt commitment letter.

If any portion of the debt financing becomes unavailable on the terms and conditions contemplated in the debt commitment letter (subject to any “market flex” provisions included in the fee letter, dated as of February 4, 2014, by and between Entegris and Goldman Sachs, and other than on account of any alternative financing), other than due to the failure of a condition to the consummation of the debt financing resulting from a material breach of any representation, warranty or covenant of ATMI set forth in the merger agreement or the failure of any of the closing conditions set forth in the merger agreement, each of Entegris and Merger Sub will use its reasonable best efforts to obtain any such portion from alternative debt or equity sources as promptly as practicable following the occurrence of such event in an amount that will still enable Entegris and Merger Sub to pay the aggregate merger consideration and any other amounts required to be paid by Entegris or Merger Sub in connection with the consummation of the transactions contemplated by the merger agreement and pay all related fees and expenses of Entegris and Merger Sub.

Entegris will keep ATMI informed on a reasonably current basis in reasonable detail of the status of its efforts to arrange the debt financing and shall provide to ATMI copies of any amendment, restatement, replacement, supplement or modification of the debt commitment letter and all executed final definitive documents relating to the debt financing (excluding any provisions related solely to fees and economic terms (other than covenants) agreed to by the parties thereto and any provisions in any fee or engagement letters as customarily excluded by the financing sources). Without limiting the generality of the foregoing, Entegris will give ATMI prompt written notice which shall include reasonably detailed information (and will, as soon as reasonably practicable, after ATMI delivers Entegris or Merger Sub a written request, provide any additional information reasonably requested by ATMI) regarding the following circumstances:

67

Table of Contents

Until the earlier of the closing date of the merger and the termination of the merger agreement, ATMI will provide, and will cause its subsidiaries to provide and will use its reasonable best efforts to cause its representatives to provide, Entegris and Merger Sub such cooperation as may be reasonably requested by Entegris in connection with any debt financing, including:

68

Table of Contents

Notwithstanding the foregoing, neither ATMI nor any of its subsidiaries will be required to take any action (A) that would cause it to bear any out-of-pocket cost or expense (not otherwise subject to reimbursement) or to pay any commitment or other similar fee or make any other similar payment or incur any other monetary liability or provide or agree to provide any indemnity in connection with the debt financing or any of the foregoing, in each case, to the extent effective prior to the effective time of the merger, (B) under the financing provision of the merger agreement that would interfere unreasonably with the business or operations of ATMI or its subsidiaries and (C) that will conflict with or violate their respective organizational documents or result in the contravention of any contract to which ATMI or any of its subsidiaries is a party that is material to the business of ATMI and its subsidiaries taken as a whole prior to the effective time of the merger (provided, however, that the foregoing clauses (B) and (C) shall not apply to or affect ATMI’s obligations under the merger agreement with respect to the delivery of the required information and certain specified actions which are usual and customary with respect to syndicated credit facilities or high yield offerings).

Entegris may make reasonable use of ATMI’s and its subsidiaries’ logos in connection with the marketing of any debt financing; provided that such logos are used solely in a manner that is not intended to, and is not reasonably likely to harm or disparage ATMI or any of its subsidiaries or the reputation or goodwill of ATMI, its subsidiaries and its or their respective marks, products, services, offerings or intellectual property rights.

Regulatory Matters

ATMI and Entegris have generally agreed to cooperate with each other and use their respective reasonable best efforts to take all actions reasonably necessary, proper or advisable to cause the conditions to the closing of the merger to be satisfied as promptly as reasonably practicable and to consummate the merger in the most expeditious manner reasonably practicable, including obtaining all approvals and consents from any governmental entity or third party necessary, proper or advisable to consummate the merger.

Each of ATMI and Entegris has agreed to make an appropriate filing of a notification and report form under the HSR Act and make any filing required under any other applicable antitrust and competition laws with respect to the transactions contemplated by the merger agreement as promptly as reasonably practicable and advisable following the date of the merger agreement (which, in the case of the notification and report form pursuant to the HSR Act, will be no later than ten business days from the date of the merger agreement and, in the case of all other filings under any other applicable antitrust and competition laws, will be as promptly as reasonably practicable following the date of the merger agreement, or, in each case, as otherwise agreed to by ATMI and Entegris), supply as promptly as practicable and advisable any additional information and documentary material that may be requested pursuant to the HSR Act or any other applicable antitrust and competition laws and to use its reasonable best efforts to cause the expiration or termination of the applicable waiting periods under the HSR Act and any other applicable antitrust and competition laws and to obtain all consents under any applicable antitrust and competition laws that may be required by the FTC, DOJ or any other governmental entity with competent jurisdiction, so as to enable ATMI, Entegris and Merger Sub to consummate the merger and other transactions contemplated by the merger agreement. In furtherance of the foregoing, each of ATMI and Entegris has agreed to defend any legal action challenging the merger agreement or the transactions contemplated thereby,

69

Table of Contents

to execute settlements, undertaking, consent decrees, stipulations or other agreements with any governmental entity or with any other person, to terminate existing relationships, contractual rights or obligations of ATMI or Entegris and to effectuate other changes or restructurings of ATMI or Entegris, in each case, to the extent necessary to obtain all consents that may be required under the HSR Act or any other applicable antitrust and competition laws or to resolve any objections asserted by any governmental entity with competent jurisdiction. Nothing in the merger agreement (W) requires Entegris or Merger Sub to sell, divest, convey or hold separate or otherwise take any other action (and ATMI will not undertake any such action without Entegris’s prior written consent) that limits Entegris’s and its subsidiaries’ freedom of action with respect to, or their ability to retain, particular products, assets or businesses of Entegris or the ATMI or their respective subsidiaries, or agree to take any such action, other than, solely in respect of products, assets or businesses of ATMI (and not, for the avoidance of doubt, any products, assets, or businesses of Entegris), only to the extent that such action would not reasonably be expected to impact in any material respect the expected benefits to Entegris and its subsidiaries, taken as a whole, of the transactions contemplated by the merger agreement, (X) requires Entegris, ATMI or their respective subsidiaries to take or agree to take any action with respect to its business or operations unless the effectiveness of such agreement or action is conditioned upon the closing, (Y) requires any of the parties to the merger agreement to compensate any third party, commence or participate in litigation or offer or grant any accommodation (financial or otherwise) to any third party to obtain any such consent or approval or (Z) permits ATMI or any of its subsidiaries to take or agree to any action or other matter pursuant to the terms of the merger agreement referred to in clauses above without Entegris’s prior written consent, not to be unreasonably withheld. Other than with respect to the payment of all filing fees in connection therewith, which will be borne solely by Entegris, the parties will each bear their own costs and expenses of preparing such notifications and filings, including the fees of their respective legal counsel.

Termination

ATMI and Entegris may terminate the merger agreement at any time before the effective time of the merger under the following circumstances:

70

Table of Contents

In addition, ATMI may terminate the merger agreement under the following circumstances:

In addition, Entegris may terminate the merger agreement under the following circumstances:

In some cases, termination of the merger agreement may require ATMI to pay a termination fee to Entegris or Entegris to pay a reverse termination fee to ATMI, in each case, as described below under “— Termination Fees and Reimbursement of Expenses.”

Except as set forth above, all fees and expenses incurred in connection with the merger and the other transactions contemplated by the merger agreement will be paid by the party incurring such fees or expenses, regardless of whether or not the merger is consummated.

71

Table of Contents

Termination Fees and Reimbursement of Expenses

ATMI Termination Fee

The merger agreement requires ATMI to pay a termination fee of $30 million to Entegris in each of the following circumstances: