X0508 4 2026-02-20 0001049502 MKS INC MKSI 0001414656 Lee John Tseng-Chung C/O MKS INC. 2 TECH DRIVE ANDOVER MA 01810 1 1 President & CEO 0 Common Stock 2026-02-20 4 S 0 13310 256.0538 D 171386.1077 D Common Stock 2026-02-20 4 S 0 12812 256.9313 D 158574.1077 D Common Stock 2026-02-20 4 S 0 1988 257.8084 D 156586.1077 D Common Stock 2026-02-20 4 S 0 1890 259.7032 D 154696.1077 D This transaction was executed in multiple trades at prices ranging from $255.425 to $256.415. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide, upon request, the full information regarding the number of shares and prices at which the transaction was effected. This transaction was executed in multiple trades at prices ranging from $256.4275 to $257.275. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide, upon request, the full information regarding the number of shares and prices at which the transaction was effected. This transaction was executed in multiple trades at prices ranging from $257.445 to $258.320. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide, upon request, the full information regarding the number of shares and prices at which the transaction was effected. This transaction was executed in multiple trades at prices ranging from $259.170 to $259.920. The price reported above reflects the weighted average sale price. The reporting person hereby undertakes to provide, upon request, the full information regarding the number of shares and prices at which the transaction was effected. /s/ M. Kathryn Rickards, attorney-in-fact 2026-02-23