In this study, quasi-enhancement mode AlGaN/GaN HEMT devices with the gate length of 1-mum are fabricated using a conventional method (i.e. without gate-recessing process) and the direct current and radio frequency characteristics of these devices are investigated. The threshold voltages are in the range of -0.3 to -0.5 V. The devices exhibit a maximum drain current of 280 mA/mm at a gate bias of 2 V. The pinch off voltage is about -1.0 V. At the gate bias of 1.5 V and the drain bias of 6 V, the devices exhibit an extrinsic transconductance of 140 mS/mm, a unity current gain cutoff frequency (f(T)) of 4.3 GHz, and a maximum oscillation frequency (f(MAX)) of 13.3 GHz, respectively. (C) 2003 Elsevier Ltd. All rights reserved.