Gallium nitride electronic devices for high-power, high-temperature applications are reviewed here. Devices ranging from heterostructure field effect transistors (HFETs) and heterojunction bipolar transistors, to Schottky and p-i-n rectifiers are discussed. The Figure shows a schematic of a planar diode fabricated with p-guard rings, such edge termination methods being shown to significantly increase reverse breakdown voltage in GaN diode rectifiers.