We report on the studies of the temperature dependence of gate–leakage current in AlGaN/GaN high-electron-mobility transistors (HEMTs) for the temperature range 20–400 °C. The results show that the temperature dependence of gate–leakage current for AlGaN/GaN HEMTs at subthreshold regime (VGS=-6.5 V) have both negative and positive trends. It has been observed that the leakage current decreases with the temperature up to 80 °C. Above 80 °C, the leakage current increases with the temperature. The negative temperature dependence of leakage current with the activation energy +0.61 eV is due to the impact ionization. The positive temperature dependence of leakage current with the activation energy -0.20 eV is due to the surface related traps, and the activation energy -0.99 eV is due to the temperature assisted tunneling mechanism. The drain voltage at a fixed drain–leakage current reveals the occurrence of both positive (+0.28 V/K) and negative (-0.53 V/K) temperature coefficients. © 2003 American Institute of Physics.