Sec Form 4 Filing - Xiao Deming @ MONOLITHIC POWER SYSTEMS INC - 2015-02-03

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

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, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Xiao Deming 2. Issuer Name and Ticker or Trading Symbol MONOLITHIC POWER SYSTEMS INC [ MPWR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Pres. of MPS Asia Operations (Last) (First) (Middle) 79 GREAT OAKS BLVD 3. Date of Earliest Transaction (MM/DD/YY) 02/03/2015 (Street) SAN JOSE, CA95119 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 02/03/2015 A 102,204 ( 1 ) A $ 0 236,357 D Common Stock 02/03/2015 S( 2 ) 2,013 D $ 47.21 234,344 D Common Stock 02/03/2015 S( 2 ) 103 D $ 47.21 234,241 D Common Stock 02/03/2015 A 8,071 ( 3 ) A $ 0 242,312 D Common Stock 02/05/2015 S 17,132 ( 2 ) D $ 47.7954 225,180 D Common Stock 02/05/2015 S 6,911 ( 2 ) D $ 47.7956 218,269 D Common Stock 02/05/2015 S 820 ( 2 ) D $ 48.0202 217,449 D Common Stock 02/03/2015 S( 2 ) 7 D $ 47.21 1,699 I by Spouse Common Stock 02/03/2015 S( 2 ) 120 D $ 47.21 1,579 I by Spouse

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underlying Securities (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 of Derivative Security: 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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Xiao Deming 79 GREAT OAKS BLVD SAN JOSE, CA95119 Pres. of MPS Asia Operations Signatures By: Saria Tseng For: Deming Xiao 02/05/2015 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On February 11, 2013, the reporting person was granted a target of 36,187 shares of restricted stock units subject to satisfaction of pre-determined, performance-based vesting criteria. On February 3, 2015, the Company's Board of Directors determined that those performance criteria for the restricted stock units had been satisfied, which resulted in 66,017 additional shares being achieved and granted to the reporting person. Of the restricted stock units that were awarded, 51,101 will vest immediately and 51,103 will vest quarterly in the next two years. ( 2 )Shares sold to pay tax obligations resulting from the vesting of restricted stock units. ( 3 )1/12 of the Restricted Stock Units shall vest quarterly following the Vesting Commencement Date, provided that the Grantee continues to be a Service Provider from the Grant Date through each applicable vesting date.

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