Abstract This paper reports on the demonstration of microwave power performance at 30 GHz on InAlN/GaN metal–insulator–semiconductor high electron mobility transistor (MISHEMT) on silicon substrate by using the Hf_0.5Zr_0.5O₂ (HZO) as a gate dielectric. Compared with Schottky gate HEMT, the MISHEMT with a gate length (L _G) of 50 nm presents a significantly enhanced performance with an ON/OFF current ratio (I _ON/I _OFF) of 9.3 × 10⁷, a subthreshold swing of 130 mV dec⁻¹, a low drain-induced barrier lowing of 45 mV V⁻¹, and a breakdown voltage of 35 V. RF characterizations reveal a current gain cutoff frequency (f _T) of 155 GHz and a maximum oscillation frequency (f _max) of 250 GHz, resulting in high (f _T × f _max)^1/2 of 197 GHz and the record high Johnson’s figure-of-merit (JFOM = f _T × BV) of 5.4 THz V among the reported GaN MISHEMTs on Si. The power performance at 30 GHz exhibits a maximum output power of 1.36 W mm⁻¹, a maximum power gain of 12.3 dB, and a peak power-added efficiency of 21%, demonstrating the great potential of HZO/InAlN/GaN MISHEMTs for the Ka-band application.