Sec Form 4 Filing - Ho Yueh-Se @ ALPHA & OMEGA SEMICONDUCTOR Ltd - 2018-03-15

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 Ho Yueh-Se 2. Issuer Name and Ticker or Trading Symbol ALPHA & OMEGA SEMICONDUCTOR Ltd [ AOSL] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Operating Officer (Last) (First) (Middle) 475 OAKMEAD PARKWAY 3. Date of Earliest Transaction (MM/DD/YY) 03/15/2018 (Street) SUNNYVALE, CA94085 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 Shares 03/15/2018 M 2,812 ( 1 ) A $ 0 272,360 ( 2 ) D Common Shares 03/15/2018 F 932 ( 3 ) D $ 16.22 271,428 ( 2 ) D Common Shares 03/15/2018 F 5,533 ( 4 ) D $ 16.22 265,895 ( 2 ) D Common Shares 03/15/2018 A 13,000 ( 5 ) A $ 0 278,895 ( 2 ) D

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 Derivati ve 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 Performance RSU $ 0 03/15/2018 M 3,125 ( 6 ) ( 6 ) ( 6 ) Common Share 3,125 $ 0 9,375 D Performance RSU $ 0 03/15/2018 A 22,000 ( 7 ) ( 7 ) ( 7 ) Common Shares 22,000 $ 0 22,000 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Ho Yueh-Se 475 OAKMEAD PARKWAY SUNNYVALE, CA94085 X Chief Operating Officer Signatures /s/ Yangbing Hong, attorney-in-fact for Yueh-Se Ho 03/19/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents the actual number of common shares issued upon vesting of performance share units ("PSU") based on the level of achievement of specified performance goals set forth in the Reporting Person's PSU agreement. ( 2 )Includes an aggregate of 39,243 shares subject to restricted share units (RSU) awards granted on March 16, 2015, March 15, 2016, March 15, 2017, and March 15, 2018, which will be issued as such units vest in accordance with their terms. ( 3 )Shares withheld to satisfy the Issuer's tax withholding obligation upon the vesting of PSU granted on March 15, 2017. ( 4 )Shares withheld to satisfy the Issuer's tax withholding obligation upon the vesting of RSU granted on March 17, 2014, March 16, 2015, March 15, 2016, and March 15, 2017. ( 5 )The RSU shall vest in equal annual installments over four (4) years from March 15, 2018, provided that the Reporting Person remains in the Issuer's service through each such vesting date. ( 6 )Represents the vesting of one-fourth (1/4) of PSUs granted on March 15, 2017 upon the achievement of specified performance goals as certified by the compensation committee of the board of directors of the Issuer on March 15, 2018. ( 7 )Each RSU represents the right to receive a specified number of common shares upon the achievement of certain performance goals of the company.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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