The effect of gate-recess length on DC and RF performance of AlGaN/GaN gate-recessed high electron mobility transistors (HEMTs) was studied. 0.15 mum gate-length AlGaN/GaN HEMTs with varying gate-recess length from 0.5 to 1.0 mum were fabricated. DC and microwave performance did not exhibit significant dependence on the gate-recess length. The devices showed a maximum drain current density as high as 1.1 A/mm, a unity gain cutoff frequency of 79 GHz, and a maximum frequency of oscillation of 125 GHz. The measured series source resistances were essentially identical for all devices, Therefore, all the gate-recessed HEMTs exhibited similar DC and RF performance. This conclusion is derived from the fact that the values of ohmic contact resistances dominated over the values of channel resistances. The nature of the breakdown in the HEMTs was also studied. The results of temperature-dependent breakdown voltage measurements suggest that the breakdown mechanism was mainly due to tunneling gate leakage currents via shallow traps. (C) 2002 Elsevier Science Ltd. All rights reserved.