In this article, Al 0.28 Ga 0.72 N/AlN/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) with Ni/Au gate metal electrode are demonstrated. NiO or Al 2 O 3 gate oxide layer is employed as a gate dielectric layer effectively decreases the gate leakage current, enhances drain current density, and transconductance, simultaneously. As compared with the metalsemiconductor (MS) Schottky-gate device, excellent characteristics are achieved for the MOS-HEMT with NiO (Al 2 O 3 ) gate oxide layer, which include maximum drain-to-source saturation current density of 626.5 (692.0) mA mm −1 , maximum transconductance of 87.6 (94.2) mS mm −1 , gate-to-drain leakage current of 1.47 × 10 −7 (8.21 × 10 −11 ) mA mm −1 , threshold voltage of −3.48 (−3.45) V, gate voltage swing of 2.88 (3.08) V, respectively. Experimentally, the MOS-HEMT with an Al 2 O 3 gate oxide layer shows good potential for signal amplification and circuit applications.