X0508 4 2025-10-25 0001280452 MONOLITHIC POWER SYSTEMS INC MPWR 0001360833 Sciammas Maurice 5808 LAKE WASHINGTON BLVD NE KIRKLAND WA 98033 false true false false EVP, WW Sales & Marketing 0 Common Stock 2025-10-25 4 A false 135520 0 A 237849 D Common Stock 9481 I Maurice Sciammas Trust FBO Oski Crew Common Stock 1699 I The Joseph Roger Sciammas 2020 Irrevocable Trust Common Stock 2000 I Rosalind Sciammas Family 2021 Trust Common Stock 9481 I Christina Sciammas Trust FBO Oski Crew Common Stock 1499 I Clement Sciammas Brokerage Account Common Stock 1499 I Rosalind Sciammas Brokerage Account Common Stock 44930 I Sciammas Family Trust Common Stock 12228 I Various Sciammas GRATs Common Stock 1699 I The Patrick Francis Sciammas 2020 Irrevocable Trust Common Stock 4015 I By Sciammas Trust 2020 Common Stock 5000 I Clement Sciammas Family 2021 Trust Common Stock 1000 I Peter Rafferty and Eric Toothill 2021Trust Common Stock 1699 I The Chloe Liliane Sciammas 2020 Irrevocable Trust On October 25, 2022, the reporting person was granted market-based restricted stock units ("MSUs") subject to the achievement of five stock price targets and relative total stockholder return percentile rank over a three-year performance and vesting period. On October 25, 2025, the Company's Compensation Committee of the Board of Directors certified and approved the achievement of the performance criteria for the MSUs, which resulted in 135,520 shares being awarded to the reporting person. All of the shares fully vested on October 25, 2025, pursuant to the grant agreement. Ending balance includes 4 shares acquired on August 15, 2025 through the Company's qualified ESPP program. /s/ Saria Tseng, attorney-in-fact for Mr. Maurice Sciammas 2025-10-27