As filed with the U.S. Securities and Exchange Commission on January 15, 2016

                                                                                                                                       File Nos. 333-179904 and 811-22649

 UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933	x
Post-Effective Amendment No. 181	x
and/or
REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940	x
Amendment No. 181	x

(Check appropriate box or boxes)

iShares U.S. ETF Trust

(Exact Name of Registrant as Specified in Charter)

c/o State Street Bank and Trust Company

1 Iron Street

Boston, MA 02210

(Address of Principal Executive Office)(Zip Code)

Registrant’s Telephone Number, including Area Code: (415) 670-2000

The Corporation Trust Company

1209 Orange Street

Wilmington, DE 19801

(Name and Address of Agent for Service)

With Copies to:

MARGERY K. NEALE, ESQ.	DEEPA DAMRE, ESQ.
WILLKIE FARR & GALLAGHER LLP	BLACKROCK FUND ADVISORS
787 SEVENTH AVENUE	400 HOWARD STREET
NEW YORK, NY 10019-6099	SAN FRANCISCO, CA 94105

It is proposed that this filing will become effective (check appropriate box):

¨     Immediately upon filing pursuant to paragraph (b)	x    On February 14, 2016, pursuant to paragraph (b)
¨        60 days after filing pursuant to paragraph (a)(1)	¨        On (date) pursuant to paragraph (a)(1)
¨        75 days after filing pursuant to paragraph (a)(2)	¨        On (date) pursuant to paragraph (a)(2)

 If appropriate, check the following box:

x The post-effective amendment designates a new effective date for a previously filed post-effective amendment.

Explanatory Note

This Post-Effective Amendment No. 181 to the Registrant’s Registration Statement on Form N-1A is being filed pursuant to paragraph (b)(1)(iii) of Rule 485 of the Securities Act of 1933, as amended (the “1933 Act”), solely for the purpose of delaying, until February 14, 2016, the effectiveness of the registration statement for the iShares iBonds Dec 2023 AMT-Free Muni Bond ETF, filed in Post-Effective Amendment No. 173 on November 2, 2015, pursuant to paragraph (a) of Rule 485 of the 1933 Act.

This Post-Effective Amendment No. 181 incorporates by reference the information contained in Parts A, B and C of Post-Effective Amendment No. 173.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, and the Investment Company Act of 1940, as amended, the Registrant certifies that it meets all the requirements for the effectiveness of this Registration Statement pursuant to Rule 485(b)(1)(iii) of the Securities Act of 1933, as amended, and has duly caused this Post-Effective Amendment No. 181 to the Registration Statement to be signed on its behalf by the undersigned, duly authorized, in the City of San Francisco and the State of California on the15th day of January, 2016.

iSHARES U.S. ETF TRUST 

By:
	Manish Mehta*
	President
	Date: January 15, 2016

Pursuant to the requirements of the Securities Act of 1933, as amended, this Post-Effective Amendment No. 181 to the Registration Statement has been signed below by the following persons in the capacities and on the date indicated.

By:
	Mark Wiedman*
	Trustee
	Date: January 15, 2016
	John E. Martinez*
	Trustee
	Date: January 15, 2016
	Cecilia H. Herbert*
	Trustee
	Date: January 15, 2016
	Charles A. Hurty*
	Trustee
	Date: January 15, 2016
	John E. Kerrigan*
	Trustee
	Date: January 15, 2016

	Robert H. Silver*
	Trustee
	Date: January 15, 2016
	Robert S. Kapito*
	Trustee
	Date: January 15, 2016
	Madhav V. Rajan*
	Trustee
	Date: January 15, 2016
	Jane D. Carlin*
	Trustee
	Date: January 15, 2016
	/s/ Jack Gee
	Jack Gee
	Treasurer
	Date: January 15, 2016
* By:	/s/ Jack Gee
	Jack Gee
	Attorney-in-fact
	Date: January 15, 2016

* Powers of Attorney, each dated March 25, 2015, for Manish Mehta, Jane D. Carlin, Charles A. Hurty, Cecilia H. Herbert, John E. Kerrigan, Robert H. Silver, John E. Martinez, Madhav V. Rajan, Mark Wiedman and Robert S. Kapito are incorporated herein by reference to Post-Effective Amendment No. 173, filed October 30, 2015.