[Form 4] MKS INC Insider Trading Activity

Rhea-AI Filing Summary

MKS Inc. (MKSI) reported insider equity activity. On 10/31/2025, the company’s EVP, GC & Secretary converted restricted stock units into common stock, acquiring 158 shares, 52 shares, 82 shares, 144 shares, and 341 shares through code “M” transactions, each RSU representing one share.

To cover FICA taxes, 777 shares were withheld in a code “F” transaction at $143.71 per share. Following these transactions, the reporting person directly beneficially owned 51,074.509 shares of common stock. Derivative holdings listed after the activity show 16,998.737 RSUs remaining.

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

OMB Number:			3235-0287
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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^*

Burke Kathleen Flaherty

(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)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	EVP, GC & Secretary

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		158	A	(1)	51,232.509	D
Common Stock	10/31/2025		M		52	A	(1)	51,284.509	D
Common Stock	10/31/2025		M		82	A	(1)	51,366.509	D
Common Stock	10/31/2025		M		144	A	(1)	51,510.509	D
Common Stock	10/31/2025		M		341	A	(1)	51,851.509	D
Common Stock	10/31/2025		F(2)		777	D	$143.71	51,074.509	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			158	(3)	(3)	Common Stock	158	(1)	17,617.737	D
Restricted Stock Unit	(1)	10/31/2025		M			52	(4)	(4)	Common Stock	52	(1)	17,565.737	D
Restricted Stock Unit	(1)	10/31/2025		M			82	(3)	(3)	Common Stock	82	(1)	17,483.737	D
Restricted Stock Unit	(1)	10/31/2025		M			144	(4)	(4)	Common Stock	144	(1)	17,339.737	D
Restricted Stock Unit	(1)	10/31/2025		M			341	(5)	(5)	Common Stock	341	(1)	16,998.737	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 2023 RSU Award accelerated to satisfy FICA taxes.

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

5. 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).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What did MKSI’s EVP report on the Form 4 dated 10/31/2025?

Multiple RSU conversions to common stock and a tax withholding sale, resulting from code “M” and code “F” transactions.

How many MKSI shares were acquired via RSU conversions on 10/31/2025?

Shares acquired were 158, 52, 82, 144, and 341, each from an RSU converting 1-to-1 into common stock.

How many MKSI shares were withheld for taxes and at what price?

A total of 777 shares were withheld at $143.71 per share to satisfy FICA taxes.

What is the officer’s MKSI common stock ownership after the transactions?

Direct beneficial ownership is 51,074.509 shares after the reported transactions.

How many MKSI RSUs remain after the transactions?

Derivative holdings show 16,998.737 RSUs remaining after the activity.

Who is the reporting person’s role at MKSI?

The reporting person is an Officer: EVP, GC & Secretary.

What do Form 4 transaction codes M and F mean here?

Code “M” indicates RSU conversion to common stock; code “F” indicates shares used to satisfy FICA taxes.