NEW YORK — The CEO of the nation's largest solar company is out, First Solar announced Tuesday, sending its shares tumbling more than 25%.

Rob Gillette, who took over at the company two years ago, becomes the latest in a series of high-level departures at First Solar Inc., based in Tempe, Ariz.

First Solar would say only that Gillette was "no longer serving as chief executive officer."

His exit comes as some of the highest-profile companies in the sector find themselves under a congressional microscope.

GOP critics have called for ending solar loan guarantees since a one-time industry favorite and recipient of a half-billion-dollar loan, Solyndra, sought bankruptcy protection in September. The government granted loan guarantees to First Solar projects this year under the same program that provided Solyndra's loan.

First Solar shares fell $14.68, or 25.33%, to $43.27 per share — the biggest one-day drop in company history, according to FactSet.

Avian Securities analyst Mark Bachman said investors fled as the company refused to explain the decision.

"We don't know if he was fired, or if he left under his own accord," Bachman said. "There's just an air of uncertainty around this company now."

In August and September, First Solar received three federal loan guarantees totaling $3 billion under the same program that paid for the $528-million loan to Solyndra.

First Solar sold each of the projects to major utilities but still plans to develop and operate them. Damien LaVera, a spokesman for the Energy Department, said the loans were made to the project, rather than to a company, which means that the project owner ultimately is responsible in case of problems.

LaVera said the Energy Department remains confident in the loans.

Board Chairman and company founder Mike Ahearn will take over temporarily as CEO, overseeing an executive team that has seen plenty of change recently. Bruce Sohn resigned as president of operations in April, and utility systems chief Jens Meyerhoff announced he was leaving in August.

Gillette, 51, a former chief executive at Honeywell Aerospace, was hired to steer the company as the entire industry headed into a tough period. Rising competition from Chinese manufacturers and a drop in panel prices slashed profits throughout the industry.