Yahoo chairman Terry Semel stepped down as chief executive in a surprise move, ending his increasingly ineffectual pursuit of online search leader Google, a losing battle that had demoralized Yahoo's shareholders and employees, an Associated Press report said. The firm appointed co-founder Jerry Yang as its new CEO and named Susan Decker as its president, the Associated Press report said.Decker, who had been touted as Semel's heir apparent, was recently promoted from Yahoo's COO to oversee the company's advertising operations, the report said.Semel, 64, will remain chairman in a non-executive role after spending the past six years running the company, it added.The shake-up unfolded less than a week after Semel faced off with shareholders disillusioned with a nearly 30% drop in Yahoo's stock price during the past 18 months as the company's financial growth fell further behind Google's torrid pace, the Associated Press report said.Signaling Semel's decision was voluntary, Yahoo said he will not receive a severance package. The former movie studio executive already has made a fortune since joining Yahoo in May 2001, having realized nearly $450 million in gains by exercising some of the stock options he received during his tenure, the Associated Press report further said.