Versum Materials (VSM) 8-K Entry into a Material Definitive Agreement

Exhibit 99.1

Versum Materials Adopts Limited Duration Shareholder Rights Plan

Business Wire

28 February 2019

TEMPE, Ariz.—(BUSINESS WIRE)—Versum Materials, Inc. (NYSE: VSM), a leading specialty materials supplier to the semiconductor industry, today announced that its Board has adopted a limited duration Shareholder Rights Plan, details of which will be contained in a Form8-K to be filed with the U.S. Securities and Exchange Commission.

The Rights Plan, which was adopted by the Board following evaluation and consultation with the Company’s advisors, is similar to plans adopted by numerous publicly traded companies. The Rights Plan is intended to promote the fair and equal treatment of all Versum shareholders and ensure that no person or group can gain control of, or influence over, Versum, through open market accumulations or other tactics potentially disadvantaging the interest of all shareholders.

Under the Rights Plan, the Rights will become exercisable if a person or group becomes the beneficial owner of 12.5% or more of the Company’s outstanding Common Stock. In the event that the Rights become exercisable due to the triggering ownership threshold being crossed, each Right will entitle its holder to purchase, at the Right’s exercise price, a number of shares of Common Stock or equivalent securities having a market value at that time of twice the Right’s exercise price. Rights held by the triggering entity will become void and will not be exercisable to purchase shares at the reduced purchase price. The Board of Directors will, in general, be entitled to redeem the Rights at $0.001 per Right at any time before the triggering ownership threshold is crossed.

The Rights Plan may be amended, redeemed or terminated by the Versum Board of Directors at any time prior to being triggered or its expiration on August 30, 2019. The Rights Plan exempts any person or group currently owning 12.5% or more of the Company’s outstanding Common Stock. However, the Rights will be exercisable if a person or group that already owns 12.5% or more of the Company’s outstanding Common Stock acquires any additional shares after the time of announcement of the Rights Plan.

The Rights Plan does not prevent any action that the Board determines to be in the best interest of the Company and its shareholders, and is structured such that it will not be triggered by the definitive merger agreement to combine the Company with Entegris, Inc., announced on January 28, 2019.

Lazard is serving as exclusive financial advisor to Versum Materials and Simpson Thacher & Bartlett LLP is serving as legal counsel.

About Versum Materials

Versum Materials, Inc. (NYSE: VSM) is a leading global specialty materials company providing high-purity chemicals and gases, delivery systems, services and materials expertise to meet the evolving needs of the global semiconductor and display industries. Derived from the Latin word for “toward,” the name “Versum” communicates the company’s deep commitment to helping customers move toward the future by collaborating, innovating and creating cutting-edge solutions.

A global leader in technology, quality, safety and reliability, Versum Materials is one of the world’s leading suppliers of next-generation CMP slurries, ultra-thin dielectric and metal film precursors, formulated cleans and etching products, and delivery equipment that has revolutionized the semiconductor industry. Versum Materials reported fiscal year 2018 annual sales of about U.S. $1.4 billion, has approximately 2,300 employees and operates 14 major facilities in Asia and the North America. It is headquartered in Tempe, Arizona. Versum Materials had operated for more than three decades as a division of Air Products and Chemicals, Inc. (NYSE:APD).

For additional information, please visithttp://www.versummaterials.com.

Forward Looking Statements

This communication contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks and uncertainties and are made pursuant to the safe harbor provisions of Section 27A of the Securities Act of 1993, as amended and Section 21E of the Securities Exchange Act of 1934, as amended. Where a forward-looking statement expresses or implies an expectation or belief as to future events or results, such expectation or belief is expressed in good faith and believed to have a reasonable basis. The words “believe” “continue,” “could,” “expect,” “anticipate,” “intends,” “estimate,” “forecast,” “project,” “should,” “may,” “will,” “would” or the negative thereof and similar expressions are intended to identify such forward-looking statements. These forward-looking statements are only predictions and involve known and unknown risks and uncertainties, many of which are beyond Versum Materials, Inc.’s (“Versum Materials”) and Entegris, Inc.’s (“Entegris”) control. Statements in this communication regarding Versum Materials, Entegris and the combined company that are forward-looking, including projections as to the anticipated benefits of the proposed transaction, the impact of the proposed transaction on Versum Materials’ and Entegris’ business and future financial and operating results, the amount and timing of synergies from the proposed transaction, and the closing date for the proposed transaction, are based on management’s estimates, assumptions and projections, and are subject to significant uncertainties and other factors, many of which are beyond Versum Materials’ and Entegris’ control. These factors and risks include, but are not limited to, (i) weakening of global and/or regional economic conditions, generally or specifically in the semiconductor industry, which could decrease the demand for Versum Materials’ and Entegris’ products and solutions; (ii) the ability to meet rapid demand shifts; (iii) the ability to continue technological innovation and introduce new products to meet customers’ rapidly changing requirements; (iv) the concentrated customer base; (v) the ability to identify, effect and integrate acquisitions, joint ventures or other transactions; (vi) the ability to protect and enforce intellectual property rights; (vii) operational, political and legal risks of Versum Materials’ and Entegris’ international operations; (viii) Entegris’ dependence on sole source and limited source suppliers; (ix) the increasing complexity of certain manufacturing processes; (x) raw material shortages and price increases; (xi) changes in government regulations of the countries in which Versum Materials and Entegris operate; (xii) the fluctuation of currency exchange rates; (xiii) fluctuations in the market price of Entegris’ stock; (xiv) the level of, and obligations associated with, Versum Materials’ and Entegris’ indebtedness; and (xv) other risk factors and additional information. In addition, material risks that could cause actual results to differ from forward-looking statements include: the inherent uncertainty associated with financial or other projections; the prompt and effective integration of Entegris’ businesses and the ability to achieve the anticipated synergies and value-creation contemplated by the proposed transaction; the risk associated with Versum Materials’ and Entegris’ ability to obtain the approval of the proposed transaction by their shareholders required to consummate the proposed transaction and the timing of the closing of the proposed transaction, including the risk that the conditions to the transaction are not satisfied on a timely basis or at all and the failure of the transaction to close for any other reason; the risk that a consent or authorization that may be required for the proposed transaction is not obtained or is obtained subject to conditions that are not anticipated; unanticipated difficulties or expenditures relating to the transaction, the response of business partners and retention as a result of the announcement and pendency of the transaction; and the diversion of management time on transaction-related issues. For a more detailed discussion of such risks and other factors, see Versum Materials’ and Entegris’ filings with the Securities and Exchange Commission, including under the heading “Risks Factors” in Item 1A of Entegris’ Annual Report on Form10-K for the fiscal year ended December 31, 2017, filed on February 15, 2018, and Versum Materials’ Annual Report on Form10-K for the fiscal year ended September 30, 2018, filed on November 21, 2018 and in other periodic filings, available on the SEC website orwww.entegris.com orwww.versummaterials.com. Versum Materials and Entegris assume no obligation to update any forward-looking statements or information, which speak as of their respective dates, to reflect events or circumstances after the date of this communication, or to reflect the occurrence of unanticipated events, except as may be required under applicable securities laws. Investors should not assume that any lack of update to a previously issued “forward-looking statement” constitutes a reaffirmation of that statement.

2

Additional Information and Where to Find It

This communication does not constitute an offer to buy or sell or the solicitation of an offer to buy or sell any securities or a solicitation of any vote or approval. This communication relates to a proposed business combination between Versum Materials and Entegris. In connection with the proposed transaction, Entegris intends to file with the Securities and Exchange Commission (the “SEC”) a registration statement on FormS-4 that will include a joint proxy statement of Versum Materials and Entegris that also constitutes a prospectus of Entegris. Each of Versum Materials and Entegris also plan to file other relevant documents with the SEC regarding the proposed transaction. No offering of securities shall be made, except by means of a prospectus meeting the requirements of Section 10 of the U.S. Securities Act of 1933, as amended. Any definitive joint proxy statement/prospectus (if and when available) will be mailed to stockholders of Versum Materials and Entegris. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT, JOINT PROXY STATEMENT/PROSPECTUS AND OTHER DOCUMENTS THAT MAY BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY IF AND WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED TRANSACTION. Investors and security holders will be able to obtain free copies of these documents (if and when available) and other documents containing important information about Versum Materials and Entegris, once such documents are filed with the SEC through the website maintained by the SEC athttp://www.sec.gov. Copies of the documents filed with the SEC by Entegris will be available free of charge on Entegris’ website athttp://www.entegris.com or by contacting Entegris’ Investor Relations Department by email atirelations@entegris.com or by phone at978-436-6500. Copies of the documents filed with the SEC by Versum Materials will be available free of charge on Versum Materials’ website athttp://investors.versummaterials.com or by phone at484-275-5907.

Participants in the Solicitation

Versum Materials, Entegris and certain of their respective directors and executive officers may be deemed to be participants in the solicitation of proxies in respect of the proposed transaction. Information about the directors and executive officers of Versum Materials are set forth in its proxy statement for its 2019 annual meeting of shareholders, which was filed with the SEC on December 20, 2018, and Versum Materials’ Annual Report on Form10-K for the fiscal year ended September 30, 2018, which was filed with the SEC on November 21, 2018. Information about the directors and executive officers of Entegris are set forth in Entegris’ proxy statement for its 2018 annual meeting of shareholders, which was filed with the SEC on March 28, 2018, and Entegris’ Annual Report on Form10-K for the fiscal year ended December 31, 2017, which was filed with the SEC on February 15, 2018. Other information regarding the participants in the proxy solicitations and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the joint proxy statement/prospectus and other relevant materials to be filed with the SEC regarding the proposed transaction when such materials become available. Investors should read the joint proxy statement/prospectus carefully when it becomes available before making any voting or investment decisions. You may obtain free copies of these documents from Versum Materials or Entegris using the sources indicated above.

Contacts

Versum Materials

Soohwan Kim, CFA

Head of Investor Relations

602-282-0957

Soohwan.Kim@versummaterials.com

Tiffany Elle

Global Communications

480-282-6475

Tiffany.Elle@versummaterials.com

Or

Meghan Gavigan / Emily Claffey / Julie Rudnick

Sard Verbinnen & Co

212-687-8080

3