=== SEC Form 4 — Statement of Changes in Beneficial Ownership ===
Document Type: 4
Period of Report: 2026-05-15
10b5-1 Pre-arranged Plan: Yes
--- Issuer ---
Name: MONOLITHIC POWER SYSTEMS INC (MPWR)
CIK: 0001280452
--- Reporting Owner ---
Name: Sciammas Maurice
CIK: 0001360833
Role: Officer (EVP, WW Sales & Marketing)
--- Non-Derivative Transactions ---
[Transaction #1]
Security: Common Stock
Date: 2026-05-15 | Code: S (Open market sale)
Shares: -3,741 | Price: $1,550.36
Total Value: $5,799,896.76
Shares Owned After: 174,903 | Ownership: D (Direct)
Footnotes:
[F1] This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
[F2] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,549.62 to $1,554.55. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #2]
Security: Common Stock
Date: 2026-05-15 | Code: S (Open market sale)
Shares: -1,717 | Price: $1,557.48
Total Value: $2,674,193.16
Shares Owned After: 173,186 | Ownership: D (Direct)
Footnotes:
[F1] This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
[F3] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,554.59 to $1,559.37. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #3]
Security: Common Stock
Date: 2026-05-15 | Code: S (Open market sale)
Shares: -2,010 | Price: $1,562.01
Total Value: $3,139,640.10
Shares Owned After: 171,176 | Ownership: D (Direct)
Footnotes:
[F1] This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
[F4] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,559.61 to $1,564.59. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #4]
Security: Common Stock
Date: 2026-05-15 | Code: S (Open market sale)
Shares: -2,020 | Price: $1,567.15
Total Value: $3,165,643.00
Shares Owned After: 169,156 | Ownership: D (Direct)
Footnotes:
[F1] This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
[F5] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,564.75 to $1,569.67. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #5]
Security: Common Stock
Date: 2026-05-15 | Code: S (Open market sale)
Shares: -1,312 | Price: $1,571.49
Total Value: $2,061,794.88
Shares Owned After: 167,844 | Ownership: D (Direct)
Footnotes:
[F1] This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
[F6] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,569.78 to $1,574.53. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #6]
Security: Common Stock
Date: 2026-05-15 | Code: S (Open market sale)
Shares: -703 | Price: $1,577.75
Total Value: $1,109,158.25
Shares Owned After: 167,141 | Ownership: D (Direct)
Footnotes:
[F1] This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
[F7] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,574.9 to $1,579.7. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #7]
Security: Common Stock
Date: 2026-05-15 | Code: S (Open market sale)
Shares: -447 | Price: $1,582.21
Total Value: $707,247.87
Shares Owned After: 166,694 | Ownership: D (Direct)
Footnotes:
[F1] This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
[F8] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,579.97 to $1,584.43. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
[Transaction #8]
Security: Common Stock
Date: 2026-05-15 | Code: S (Open market sale)
Shares: -50 | Price: $1,585.51
Total Value: $79,275.50
Shares Owned After: 166,644 | Ownership: D (Direct)
Footnotes:
[F1] This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
[F9] The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,585.17 to $1,586.76. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
--- Holdings ---
[Holding #1]
Security: Common Stock
Ownership: I (Indirect)
[Holding #2]
Security: Common Stock
Ownership: I (Indirect)
[Holding #3]
Security: Common Stock
Ownership: I (Indirect)
[Holding #4]
Security: Common Stock
Ownership: I (Indirect)
[Holding #5]
Security: Common Stock
Ownership: I (Indirect)
[Holding #6]
Security: Common Stock
Ownership: I (Indirect)
[Holding #7]
Security: Common Stock
Ownership: I (Indirect)
[Holding #8]
Security: Common Stock
Ownership: I (Indirect)
[Holding #9]
Security: Common Stock
Ownership: I (Indirect)
[Holding #10]
Security: Common Stock
Ownership: I (Indirect)
[Holding #11]
Security: Common Stock
Ownership: I (Indirect)
--- Footnotes (Complete Index) ---
F1: This transaction was made pursuant to a Rule 10b5-1 trading plan adopted on 11/24/2025.
F2: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,549.62 to $1,554.55. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F3: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,554.59 to $1,559.37. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F4: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,559.61 to $1,564.59. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F5: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,564.75 to $1,569.67. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F6: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,569.78 to $1,574.53. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F7: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,574.9 to $1,579.7. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F8: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,579.97 to $1,584.43. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
F9: The price is the weighted average sale price for the transactions reported on this line. The prices for the transactions reported on this line range from $1,585.17 to $1,586.76. The reporting person undertakes to provide, upon request by the staff of the Securities and Exchange Commission, the issuer, or a security holder of the issuer, full information regarding the number of shares sold at each separate price.
--- Signature ---
/s/ /s/ Saria Tseng, attorney-in-fact for Mr. Maurice Sciammas (2026-05-19)
