The effects of post gate annealing on microwave noise performance of AlGaN/GaN HEMTs on SiC substrate were investigated. The results show that post Schottky gate annealing under an optimized condition, 400 degrees C for 10 min in N-2 ambient, can increase the current driving capability, reduce gate leakage current, and improve the microwave noise performance. Specifically, the maximum extrinsic transconductance increased from 223 mS/mm to 233 mS/mm. The I mA/mm gate leakage current at V-gs = - 30 V reduced to 4 nA/mm. Before annealing, the device exhibited a minimum noise figure of 0.99 dB at 4 GHz. It decreased to 0.63 dB and the associated gain increased from 13.2 dB to 17.4 dB at the mean time. The change is even more significant under high current operation. At 4 GHz, the 4.90 dB NFmin at I-ds of 670 mA/mm decreased more than 3 dB to 1.12 dB. Based on a simple noise model, the improvement of the microwave noise performance is attributed to the significant decrease of the gate leakage current. (c) 2006 Elsevier Ltd. All rights reserved.