In a letter he sent to ""the Apple community"" on Wednesday (24Aug11), Jobs revealed he felt he could no longer handle the job.
He took an indefinite leave of absence from the company at the beginning of 2011 to battle an undisclosed medical issue. It was his third medical leave in recent years.
Jobs has remained frail since surviving pancreatic cancer in 2009.
In his letter to Apple employees, he wrote, ""I have always said if there ever came a day when I could no longer meet my duties and expectations as Apple's CEO, I would be the first to let you know. Unfortunately, that day has come.""
Tim Cook will replace him as CEO. Jobs will serve the electronics company as board chairman.