On the basis of AlGaN/GaN HEMT，the AlGaN/GaN MOSHEMT device was fabricated with Al2O3 insulating film for the first time, which was deposited by ALD.The X-ray photoelectron spectroscopy measurements showed successful deposition of Al2O3 layer on the AlGaN/GaN film. The results of Schottky capacitance，I-V characteristics and DC transfer characteristics measurement showed that the interface state density between the AlGaN film and the Al2O3 insulating film was fairly low and the MOSHEMT device showed successful gate control of drain current up to VGS=+3V and achieved drain saturation current of 800mA/mm，which was much larger than that of the HEMT device. Furthermore，the gate leakage current of MOSHEMT is two orders lower in the reverse bias condition as compared with the Schottky gate structure，which increased the device breakdown voltage，while the leakage current was governed by the Fowler-Nordheim tunneling mechanism.