Shares of Amkor Technology Inc. climbed Thursday, after the semiconductor-testing company posted an unexpectedly high third-quarter profit with help from strong demand.

The Chandler, Ariz.-based company also indicated a slowdown in fourth-quarter sales wouldn't be as severe as expected.

Amkor's stock rose $1.05, or 14 percent, to $8.54 in early afternoon trading on the Nasdaq Stock Market. Thursday's strongest level, on heavy volume, was $8.69. On a 52-week basis, there was a high of $13.09 on April 27 and a low of $4.61 on Sept. 27.

Late Wednesday, Amkor said it moved to a third-quarter profit of $52.8 million, or 27 cents a share, from a loss of $19.5 million, or 11 cents a share, a year earlier. Analysts surveyed by Thomson Financial had forecast, on average, earnings of about 24 cents a share.

Revenue surged 30 percent to $713.8 million from $549.6 million, amid seasonal demand from makers of wireless and mobile devices, gaming consoles and other products.

For the fourth quarter, the company expects to post per-share earnings of 20 cents to 24 cents, as compared to the 21 cents that had been expected by Wall Street.

The company also expects sales of $678.1 million to $692.4 million _ still topping the roughly $676.9 million expected by analysts.

In a research note, Lehman Brothers analyst David Egan said he expected a fourth-quarter downturn for semiconductor subcontractors after several quarters of growth because of the cyclical nature of the business. He said the assembly and testing companies were avoiding price increases that hurt business during cyclical troughs in the past.

"Looking forward, we currently believe that there is reason to think that this improved financial performance is sustainable into the downturn and over the next cycle," Egan said.