AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) using a radio-frequency magnetron sputtered ZrZnO transparent oxide layer as a gate insulator are investigated and compared with traditional GaN HEMTs. A negligible hysteresis voltage shift in the C–V curves is seen, from 0.09V to 0.36V, as the thickness of ZrZnO films increases. The composition of ZrZnO at different annealing temperatures is observed using X-ray photoelectron spectroscopy (XPS). The ZrZnO thin film achieves good thermal stability after 600°C, 700°C and 800°C post-deposition annealing (PDA) because of its high binding energy. Based on the interface trap density analysis, D it has a value of 2.663×10 12 cm −2 /eV for 10-nm-thick ZrZnO-gate HEMTs and demonstrates better interlayer characteristics, which results in a better slopes for the I ds degradation (5.75×10 −1 mA/mmK −1 ) for operation from 77K to 300K. The 10-nm-thick ZrZnO-gate device also exhibits a flat and a stable 1/f noise, as V GS –V th , and at various operating temperatures. Therefore, ZrZnO has good potential for use as the transparent film for a gate insulator that improves the GaN-based FET threshold voltage and improves the number of surface defects at various operating temperatures.