Employing Ga2O3(Gd2O3) as gate dielectric and Si-doped GaAs as conducting channel, depletion-mode GaAs MOSFETs were fabricated. DC I-V and transfer curves show no pinch-off and drain current hysteresis. Etching a thin layer from the top of Ga2O3(Gd2O3) in the gate region before gate metal deposition leads to full pinch-off and significantly reduces the drain current hysteresis. This process may remove the contaminated Ga2O3(Gd2O3) due to exposure to chemicals and prior processes, and thus results in a clean gate metal to oxide interface. The clean gate metal to Ga2O3(Gd2O3) interface also leads to higher DC transconductance, higher unity current gain cut-off frequency as well as higher unity power gain cut-off frequency as compared with GaAs MOSFET devices with a contaminated metal/oxide interface at the gate. (C) 2002 Elsevier Science B.V. All rights reserved.