By Poornima Gupta | Reuters

SAN FRANCISCO (Reuters) - Silicon Valley legend Steve Jobs on Wednesday resigned as chief executive of Apple Inc in a stunning move that ended his 14-year reign at the technology giant he co-founded in a garage.

Apple shares dived as much as 7 percent in after-hours trade after the pancreatic cancer survivor and industry icon, who has been on medical leave for an undisclosed condition since January 17, announced he will be replaced by COO and longtime heir apparent Tim Cook.

Analysts do not expect Jobs' resignation -- which had long been foreseen -- to derail the company's fabled product-launch roadmap, including possibly a new iPhone in September and a third iteration of the iPad tablet in 2012.

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"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," he said in a brief letter announcing his resignation.

The 55-year-old CEO had briefly emerged from his medical leave in March to unveil the latest version of the iPad and later to attend a dinner hosted by President Barack Obama for technology leaders in Silicon Valley.

Jobs' often-gaunt appearance has sparked questions about his health and his ability to continue at Apple.

"I will say to investors: don't panic and remain calm, it's the right thing to do. Steve will be chairman and Cook is CEO," said BGC Financial analyst Colin Gillis.

Apple shares slid to $357.40 in extended trading after a brief halt. They had gained 0.7 percent to close at $376.18 on the Nasdaq.

Analysts again expressed confidence in the Apple bench, headed by longtime company No. 2 and supply-chain maven Cook.

"Investors are very comfortable with Tim Cook even though Jobs has been a driver of innovation and clearly an Apple success. Tim has shown Apple can still outperform extremely well when he's been acting as CEO," said Cross Research analyst Shannon Cross.

"I don't know if it's a health issue. I don't know if it is a shock. Most likely it was going to happen at some point. Why today versus another day? I don't know."

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(Reporting by Poornima Gupta and Edwin Chan; Editing by Gary Hill)