Two depletion-mode GaAs-based metal-oxide-semiconductor field-effect transistor (MOSFETs) were made with molecular beam epitaxy (MBE) grown Ga2O3(Gd2O3) as the gate dielectric on different channel structures. The depletion-mode GaAs MOSFETs with a gate length of 1.6 mu m show an accumulated drain current density of 335 mA/mm at V-G up to 4 V. The In0.15Ga0.85As/GaAs MOSFET, with a 4-angstrom-thick amorphous Si cap layer exhibits a large drain current density of 5 10 mA/mm at V-G up to 2 V. The output characteristics measured by a curve tracer show no I-V hysteresis and drain current drift. These excellent device characteristics were resulted from a high-quality, low-trap interface between Ga2O3(Gd2O3) and the channels. (c) 2007 Elsevier B.V. All rights reserved.