AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with Al2O3 gate oxide which was deposited by atomic layer deposition (ALD) were fabricated and their performance was then compared with that of AlGaN/GaN MOSHFETs with HfO2 gate oxide. The capacitance (C)voltage (V) curve of the Al2O3/GaN MOS diodes showed a lower hysteresis and lower interface state density than the C-V curve of the HfO2/GaN diodes, indicating better quality of the Al2O3/GaN interface. The saturation of drain current in the I-D-V-GS relation of the Al2O3 AlGaN/GaN MOSHFETs was not as pronounced as that of the HfO2 AlGaN/GaN MOSHFETs. The gate leakage current of the Al2O3 MOSHFET was five to eight orders of magnitude smaller than that of the HfO2 MOSHFETs. (C) 2011 Elsevier Ltd. All rights reserved.