The influence of temperature (-50 degrees C to +200 degrees C) was studied on the DC and microwave characteristics of AlGaN/GaN high-electronmobility transistors (HEMTs) on high resistivity Si substrate for the first time. The AlGaN/GaN HEMTs exhibited a current-gain cut-off frequency (f(T)) of 11.8 GHz and maximum frequency of oscillation (f(max)) of 27.5 GHz. When compared to room temperature values, about 4% and 10% increase f(T) and f(max) and 23% and 39.5% decrease f(T) and f(max) were observed when measured at -50 'C and 200 degrees C, respectively. The improvement of I-D, g(m)f(T), and f(max) at -50 degrees C is due to the enhancement of 2DEG mobility and effective electron velocity. The anomalous drain current reduction in the I-V curves were observed at low voltage region at the temperature <= 10 degrees C but disappeared when the temperature reached >= 25 degrees C. A positive threshold voltage (V-th) shift was observed from -50 degrees C to 200 degrees C. The positive shift of V-th is due to the occurrence of trapping effects in the devices. The drain leakage current decreases with activation energies of 0.028 eV and 0.068 eV. This decrease of leakage current with the increase of temperature is due to the shallow acceptor initiated impact ionization. (c) 2006 Elsevier B.V. All rights reserved.