Intel Corp. was hit with the surprise departure of its longtime chief executive as the company, which makes most of the chips found in personal computers, pushes to restore its sway over the high-tech sector amid an industry shift to smartphones and other mobile devices.

Paul Otellini, Intel's CEO since 2005 and a fixture in Silicon Valley, informed the board on Wednesday that he wanted to retire in May. The 62-year-old had widely been expected to stay in his position until Intel's...