A metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT) with atomic layer deposition (ALD) of 10nm Al2O3 gate dielectric is manufactured. The superiorities in saturation current and leakage current of the novel MOS-HEMT device are verified by comparison of the MOS-HEMT with traditional MES-HEMT devices at room temperature. The statistical analysis of the features of temperature variation of the device characteristics in the 30—180℃ range, which shows the distinction in degration degree by temperature on the two kinds of devices, is also illustrated. The conclusion that the device saturation current and the transconductance degradations are mainly caused by transport characteristic degradation is reached at. Thus, the conclusion can be drawn that all statistical and analytical results witness the significant role played by the reduced surface states in the surface of the AlGaN in optimizing the characteristics of the device.