Daniel Kunz quit April 19 after a decade at the helm of the Boise company.
Kunz will be succeeded by Dennis Gilles, 54, a U.S. Geothermal board member and a former executive at Calpine Corp. who helped oversee that companys geothermal business. Gilles retired from Calpine in 2011.
U.S. Geothermal now has three operating power plants, including its new Neal Hot Springs project in eastern Oregon, which in recent months began generating 28 megawatts of electricity, enough to power 25,000 to 28,000 homes. It also has plants near Malta and Gerlach, Nev.
The company has 45 employees.
Kunz plans to serve as a consultant to the company for a year after his departure.