EXHIBIT 23a CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS As independent public accountants, we hereby consent to the incorporation by reference of our report dated January 28, 2000 included in Mid-State Bancshares' 1999 Form 10-K for the three years ended December 31, 1999, into the previously filed S-8 registration statement File No. 333-29161. /s/ Arthur Andersen LLP ARTHUR ANDERSEN LLP Orange County, California June 2, 2000