The DC characteristics of AlGaN/GaN HFETs on Si substrates are reported as a function of temperature and gate length. Stable operation up to 500 degrees C was obtained with no significant permanent degradation. The temperature dependence of the saturation current was found to follow a power law of T-1.5 for long channel devices, but improved to show only a weak T-0.5 dependence for submicron gate length devices. (c) 2006 Elsevier Ltd. All rights reserved.