SEATTLE (AP) - Apple Inc. co-founder and CEO Steve Jobs is back at work after a five-and-a-half-month medical leave, during which he received a liver transplant.

Jobs, 54, is working from Apple's Cupertino, Calif., headquarters "a few days a week" and working from home the remaining days, Apple spokesman Steve Dowling said Monday.

The Apple chief was diagnosed with a rare form of pancreatic cancer. He had surgery in 2004 and announced then that he was cured.

Last year, Jobs' dramatic weight loss prompted new questions about his health. In early January, he said in a statement that he was suffering from an easily treated hormone imbalance, but less than two weeks later Jobs said his medical condition was more complex than he initially thought. He announced he would take a leave of absence until the end of June.

Methodist University Hospital Transplant Institute in Memphis, Tenn., said last week that Jobs had received a liver transplant, confirming an earlier report in The Wall Street Journal.

Jobs was recovering well and his prognosis was good, the hospital said.

Few CEOs are considered as instrumental to their companies as Jobs has been to Apple since he returned in 1997 after a 12-year hiatus. With Jobs serving as head showman and demanding elegance in product design, Apple has expanded from a niche computer maker to become the dominant producer of portable music players and a huge player in the cell phone business.

News and rumors about his health have sent Apple stock soaring or plunging.

Shares of Apple rose 43 cents to $142.87 in afternoon trading Monday.

(Copyright 2009 by The Associated Press. All Rights Reserved.)