Wide bandgap, high saturation velocity, and high thermal stability are some of the properties of GaN, which make it an excellent material for high-power, high-frequency, and high-temperature applications. As several application areas require the devices to operate at elevated temperatures, a proper modeling of the temperature dependences of the band structure and transport parameters is very important. We present two-dimensional hydrodynamic simulations of AlGaN/GaN high electron mobility transistors (HEMTs) at high temperatures. The simulator is calibrated against measurement data of a real device and delivers good predictive results for the DC and RF characteristics of another. The temperature dependence of the maximum current and cut-off frequency of submicron devices is further studied. (C) 2010 Elsevier Ltd. All rights reserved.