Advanced Micro Devices Inc said Chief Financial Officer Thomas Seifert was leaving the struggling personal computer chipmaker to pursue other opportunities, sending its shares down almost 12 percent.

After filling in as AMD's temporary CEO through August last year, Seifert now wants to find a permanent CEO position, a source close to the company said.

Seifert's departure is concerning because he had more experience at AMD than other top executives, said Evercore Partners analyst Patrick Wang.

"Thomas leaving is a big deal. He was pretty well-liked by investors. He was viewed as he rock throughout all the changes," Wang said.

Devinder Kumar, senior vice president and corporate controller, will serve as AMD's temporary CFO until a replacement is found.

"Seifert's departure is not based on any disagreement over the company's accounting principles or practices, or financial statement disclosures," AMD said in a statement.

In July, AMD slashed its outlook for second-quarter revenue after disappointing sales in China and Europe, becoming one of the biggest tech names to date to warn that a global economic slowdown is taking a harsher-than-expected toll.

PC-related companies have been hit by a slump in demand as smartphones and tablets grow in popularity, but AMD's woes are also seen as at least partly company-specific, with executives and analysts pointing to problems with execution.

After the board ousted previous CEO Dirk Meyer, over disappointment with AMD's limited success in developing products for the smartphone and mobile markets, Seifert stood in for several months until Read was hired.

Forty-eight year-old Seifert had agreed to stay on while Read, who was previously president and chief operating officer at Lenovo, was brought up to speed, the source said.

Seifert will stay on through September 28, AMD said.

AMD shares fell 11.72 percent in extended trading after closing up 2.82 percent at $4.01.