[Form 4] MKS INC Insider Trading Activity

Rhea-AI Filing Summary

MKS Inc. (MKSI) reported insider activity by its President & CEO and Director on 10/31/2025. The filing shows RSU settlements and a related tax transaction. The executive converted RSUs into common stock under code M, acquiring 352 shares and 1,651 shares. To cover FICA taxes, 2,003 shares were disposed under code F at $143.71 per share.

Following these transactions, the executive directly owned 147,269.5227 shares. Each RSU represents the right to receive one common share. The company notes that portions of the 2024 and 2025 RSU awards were accelerated to satisfy FICA taxes.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Lee John Tseng-Chung

(Last) (First) (Middle)

C/O MKS INC.

2 TECH DRIVE

(Street)

ANDOVER MA 01810

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
MKS INC [ MKSI ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	President & CEO

3. Date of Earliest Transaction (Month/Day/Year)
10/31/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	10/31/2025		M		352	A	(1)	147,621.5227	D
Common Stock	10/31/2025		M		1,651	A	(1)	149,272.5227	D
Common Stock	10/31/2025		F(2)		2,003	D	$143.71	147,269.5227	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Restricted Stock Unit	(1)	10/31/2025		M			352	(3)	(3)	Common Stock	352	(1)	89,803.622	D
Restricted Stock Unit	(1)	10/31/2025		M			1,651	(4)	(4)	Common Stock	1,651	(1)	88,152.622	D

Explanation of Responses:

1. Each restricted stock unit (RSU) represents the contingent right to receive one share of common stock of MKS Inc.

2. Shares used to satisfy FICA taxes.

3. Portion of 2024 RSU Award accelerated to satisfy FICA taxes.

4. Portion of 2025 RSU Award accelerated to satisfy FICA taxes.

	/s/ M. Kathryn Rickards, attorney-in-fact	11/04/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
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FAQ

What did MKSI’s CEO report on Form 4?

On 10/31/2025, the CEO reported RSU settlements (codes M) and a tax-related share disposition (code F).

How many MKSI shares were acquired via RSU settlements?

The executive acquired 352 shares and 1,651 shares through RSU conversions.

How many shares were used to satisfy taxes and at what price?

A total of 2,003 shares were disposed at $143.71 per share to satisfy FICA taxes.

What is the executive’s ownership after these transactions?

Direct beneficial ownership is 147,269.5227 MKSI shares after the reported transactions.

What do the transaction codes mean in this context?

Code M reflects RSU conversions into common stock; code F reflects shares used to satisfy FICA taxes.

Were specific RSU awards referenced?

Yes. Portions of the 2024 and 2025 RSU awards were accelerated to satisfy FICA taxes.