MKS INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

Check the appropriate box:

MKS Inc.

(Name of Registrant as Specified in its Charter)

Payment of Filing Fee (Check all boxes that apply):

Dear Shareholder:

You are cordially invited to attend the 2026 Annual Meeting of Shareholders of MKS Inc. 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.

The attached notice of the Annual Meeting and proxy statement describe the business to be transacted at the Annual Meeting and provide additional information about us that you should know when voting your shares. The principal business at the Annual Meeting will be (i) the election of three Directors, each for a one-year term, (ii) the approval of the Amended and Restated 2022 Stock Incentive Plan, (iii) the approval, on an advisory basis, of executive compensation, (iv) the ratification of the selection of PricewaterhouseCoopers LLP as our independent registered public accounting firm for the year ending December 31, 2026, (v) the approval, on an advisory basis, of a Company proposal to reduce the threshold percentage of shareholders required to call a special meeting of shareholders from 40% to 25%, and (vi) the consideration of a shareholder proposal to reduce the threshold percentage of shareholders required to call a special meeting of shareholders from 40% to 10%, if properly presented at the meeting.

Whether or not you plan to attend the Annual Meeting, please carefully review the attached proxy materials and take the time to cast your vote.

On behalf of MKS, I would like to express our appreciation for your continued interest in our Company.

Sincerely,

JOHN T.C. LEEPresident and Chief Executive Officer

NOTICE OF 2026 ANNUAL MEETING OF SHAREHOLDERS

TO BE HELD ON MONDAY, MAY 11, 2026 at 10:00 A.M. EASTERN TIME

To our Shareholders:

The 2026 Annual Meeting of Shareholders of MKS Inc., a Massachusetts corporation, will be held on Monday, May 11, 2026 at 10:00 a.m., Eastern Time, at our headquarters at 2 Tech Drive, Andover, Massachusetts 01810, for the following purposes:

The shareholders will also act on any other business as may properly come before the meeting.

We provide access to our proxy materials over the Internet under the U.S. Securities and Exchange Commission’s “notice and access” rules. 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, and it 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.

The Board of Directors has fixed the close of business on March 3, 2026 as the record date for the determination of shareholders entitled to notice of, and to vote at, the Annual Meeting and any adjournment or postponement thereof. Your vote is important no matter how many shares you own. Whether or not you expect to attend the meeting, we urge you to vote your shares.

If you are a shareholder of record, you may vote by using the Internet or calling the toll-free telephone number as described in the instructions included in your Notice, or, if you received a paper copy of the proxy materials, by completing, signing, dating, and returning your proxy card or voting instruction card. If you are a beneficial shareholder (meaning the shares you own are held in “street name” by a bank, broker, or other nominee), you may vote by following the instructions your bank, broker, or other nominee provides to you. Your prompt response is necessary to ensure that your shares are represented at the meeting. You can change your vote and revoke your proxy any time before the polls close at the meeting by following the procedures described in the accompanying proxy statement.

By Order of the Board of Directors,

KATHLEEN F. BURKESecretary

Andover, Massachusetts