AlGaN/GaN high electron mobility transistor (HEMT) with ZnO gate interlayer layer was proposed in this work. It markedly suppressed the gate leakage current and enhanced microwave performances due to the matched lattice constant for insulator and semiconductor. After 2 min 600 degrees C annealing, the x-ray diffraction analysis indicates that ZnO thin films achieved a highly crystalline characteristic, which exhibited a similar lattice constant (a = 3.2498, c = 5.2066) to GaN (a = 3.1890, c = 5.1855). This ZnO thin film also shows a good thermal stability after 500, 600, and 700 degrees C postdeposition annealing due to its high binding energy (1022.35 eV) characteristics. By capacitance-voltage and low-frequency noise measurements, ZnO-gate HEMT shows a negligible hysteresis and a low surface state density. At 2.4 GHz operation, the power-added efficiency (PAE) was 31.27%, and the linear power gain (G(p)) was 16.6 dB for ZnO-gate HEMT. In contrary, PAE was 23%, and G(p) was 14 dB for the conventional device. These measured results elucidated that a high quality ZnO/GaN interface was suitable for developing a high performance GaN HEMT. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3533712] All rights reserved.