WASHINGTON — First Solar, the largest US solar panel maker, abruptly replaced chief executive Robert Gillette without explanation Tuesday.

Amid turmoil in an oversupplied industry under assault from cheaper manufacturers in China and elsewhere, First Solar said in a short statement that chairman and company founder Mike Ahearn would serve as acting chief executive, until a replacement can be found.

"The board of directors has formed a search committee and is initiating a search for a permanent chief executive officer," the statement said.

The Tempe, Arizona-based company, formed in 1999, recruited Gillette in 2009 from Honeywell Aerospace, where he had been chief executive.

The company's share price had sunk by about two-thirds this year since hitting a peak of $175.45 in February.

The shares fell another 25.3 percent to $43.27 after the announcement Tuesday.

Analysts voiced surprise at Gillette's exit.

"It's not clear why he?s leaving," said Shayle Kann, a solar industry expert at GTM Research.

"First Solar fundamentally still has the best cost structure of any manufacturer globally... Their prospects are still good."

But First Solar's sales and net income have been falling with the increase in supply from competitors and the sharp slowdown in the European market, especially in Germany.

Kann said the entire industry is under pressure.

"We hit a real massive oversupply situation. Every manufacturer everywhere is getting squeezed."

Earlier this year First Solar put on hold a major investment in a solar panel factor near Bordeaux, France, as the European market turned soft.