The use of Ag in the gate region of AlGaN/GaN heterostructure diodes is shown to provide stable, reversible changes in barrier height and thus current during exposure to ethanol at 250 degrees C. The exposed ethanol molecules are adsorbed on the silver and oxidized, resulting in the increase of Schottky barrier height. The detection limit of ethanol at this temperature was 58 ppm, and the sensor response was linear over the range 58-58700 ppm. For the high end of this concentration range (5.87%), ethanol exposure at 250 degrees C caused the Schottky barrier height to change from 0.604 eV to 0.656 eV, which produced a forward current relative change of 45.4% at 0.9V forward bias. The results are competitive with detection of ethanol by oxide thin films or nanostructures of SnO2, Fe2O3, CuO, and ZnO. (C)The Author(s) 2017. Published by ECS.