EXHIBIT 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in Registration Statement Nos. 333-195456, 333-187690, 333-160371, 333-160370, 333-145207, 333-144811, 333-135439, 333-125298, 333-120131, 333-100420 and 33-95766 on Form S-8 of our reports dated February 27, 2015, relating to the consolidated financial statements of Columbia Banking System, Inc., and the effectiveness of Columbia Banking System, Inc.’s internal control over financial reporting, appearing in the Annual Report on Form 10-K of Columbia Banking System, Inc., for the year ended December 31, 2014.

/s/ Deloitte & Touche LLP

Seattle, Washington

February 27, 2015