This work investigates an AlGaN/GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with ultrasonic spray pyrolysis (USP) deposited Al2O3. The temperature-dependent electrical characteristics like IGD-VGD, IDS-VDS, and IDS-VGS are measured from 300 K to 480 K. The MOS-HEMT shows lower IGD and higher IDS and higher gm, max. Furthermore, the MOS-HEMT has better thermal stability in electrical performances. The thermal models of electron mobility of the Al2O3/AlGaN/GaN MOS-HEMT and the AlGaN/GaN Schottky-gate HEMT with Al2O3 passivation are analyzed. The superior high-temperature electrical performances of the MOS-HEMT are very promising for highpower and high-temperature electronics applications.