Ownership Submission
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 OF SECURITIES

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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(Print or Type Responses)
1. Name and Address of Reporting Person *
Hsing Michael
  2. Issuer Name and Ticker or Trading Symbol
MONOLITHIC POWER SYSTEMS INC [MPWR]
5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
CEO
(Last)
(First)
(Middle)
79 GREAT OAKS BLVD
3. Date of Earliest Transaction (Month/Day/Year)
04/01/2015
(Street)

SAN JOSE, CA 95119
4. If Amendment, Date 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
(City)
(State)
(Zip)
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 04/01/2015   M(1)   14,117 A $ 15.03 1,052,008 D  
Common Stock 04/01/2015   S(1)   9,438 D $ 52.0002 (2) 1,042,570 D  
Common Stock 04/01/2015   M(1)   74,154 A $ 15.03 1,116,724 D  
Common Stock 04/01/2015   S(1)   49,572 D $ 52.0151 (3) 1,067,152 D  
Common Stock 04/02/2015   M(1)   107,030 A $ 15.03 1,174,182 D  
Common Stock 04/02/2015   S(1)   71,550 D $ 52.0021 (4) 1,102,632 D  
Common Stock               29,000 I Hsing Fam Foundation
Common Stock               133,040 I by M Hsing 04 Trust

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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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 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
Non-Qualified Stock Option (right to buy) $ 15.03 04/01/2015   M(1)     14,117 12/28/2012(5) 10/28/2015 Common Stock 14,117 $ 0 0 D  
Non-Qualified Stock Option (right to buy) $ 15.03 04/01/2015   M(1)     74,154 10/28/2010(6) 10/28/2015 Common Stock 74,154 $ 0 225,846 D  
Non-Qualified Stock Option (right to buy) $ 15.03 04/02/2015   M(1)     107,030 10/28/2010(6) 10/28/2015 Common Stock 107,030 $ 0 118,816 D  

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
Hsing Michael
79 GREAT OAKS BLVD
SAN JOSE, CA 95119
  X     CEO  

Signatures

 /s/ Saria Tseng For: Michael Hsing   04/03/2015
**Signature of Reporting Person Date

Explanation of Responses:

* 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).
(1) In accordance with the reporting person's 10b5-1 trading plan.
(2) 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 $52.00 to $52.02. 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.
(3) 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 $52.00 to $52.60. 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.
(4) 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 $52.00 to $52.05. 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.
(5) Original option grant was for 14,117 shares. One-hundred percent (100%) of the Shares subject to the Option shall vest immediately. All outstanding options have fully vested.
(6) Original option grant was for 300,000 shares. Fifty percent (50%) of the Shares subject to the Option shall vest twenty-four (24) months after the Vesting Commencement Date, and 1/48 of the Shares subject to the Option shall vest monthly thereafter on the same day of the month as the Vesting Commencement Date, subject to the Optionee continuing to be a Service Provider on such dates. All outstanding options have fully vested.

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