MKS INC

This proxy statement is furnished in connection with the solicitation of proxies by the Board of Directors of MKS Inc., a Massachusetts corporation, for use at the 2026 Annual Meeting of Shareholders to be held on Monday, May 11, 2026 at 10:00 a.m., Eastern Time, at our headquarters at 2 Tech Drive, Andover, Massachusetts 01810, and at any adjournment or postponement thereof, which we refer to as the 2026 Annual Meeting. References in this proxy statement to “we,” “us,” the “Company,” or “MKS” refer to MKS Inc. and its consolidated subsidiaries.

All proxies will be voted in accordance with the applicable shareholder’s instructions. If no choice is specified in the proxy, the shares will be voted in accordance with the recommendations of our Board of Directors. The Board of Directors recommends that you vote FOR each director nominee, FOR each of Proposals 2, 3, 4, and 5, and AGAINST the shareholder proposal in Proposal 6. Any proxy may be revoked by a shareholder at any time before its exercise by delivery of written revocation to the Secretary of MKS or by voting during the 2026 Annual Meeting. Attendance at the 2026 Annual Meeting will not in itself be deemed to revoke a proxy.

We provide access to our proxy materials over the Internet under the “notice and access” rules of the U.S. Securities and Exchange Commission, which we refer to as the SEC. As a result, we mail to our shareholders a Notice of Internet Availability of Proxy Materials, which we refer to as the Notice. We are mailing the Notice on or about March 31, 2026. The Notice contains instructions on how to access the proxy statement and our Annual Report for the fiscal year ended December 31, 2025, which we refer to as the 2025 Annual Report, over the Internet. The Notice also contains instructions on how our shareholders can receive a paper copy of our proxy materials, including this proxy statement, our 2025 Annual Report, and a form of proxy card or voting instruction card. All shareholders who do not receive the Notice, including shareholders who have previously requested to receive paper copies of proxy materials, will receive a paper copy of the proxy materials by mail unless they have previously requested delivery of proxy materials electronically.

Important notice regarding the availability of proxy materials for the 2026 Annual Meeting to be held on May 11, 2026: This proxy statement and the 2025 Annual Report are available for viewing, printing, and downloading free of charge atinvestor.mks.com/annual-meeting-materials.