Santa Clara, Calif.--Yahoo! Inc. announced that it has hired Terry Semel as its new chairman-CEO. Semel, a high-profile media executive who formerly was co-CEO of Warner Bros. Inc., will oversee all Yahoo!'s operations. He replaces Tim Koogle, who had stepped down as CEO last August but retained his title as chairman. Koogle will stay on with Yahoo! as vice-chairman. Semel's appointment comes soon after Yahoo! announced it would ax 3,510 jobs, or 12% of its work force.