A comprehensive study of an InAlAs/InGaAs metal-oxide-semiconductor metamorphic high electron mobility transistor (MOS-MHEMT) with liquid-phase-oxidized InAlAs as gate insulators has been demonstrated. The MOS-MHEMT exhibits a lower leakage current density with suppressed impact ionization effect, better microwave characteristics, and improved noise performance in comparison with the conventional Schottky gate metamorphic high electron mobility transistor. The unity current gain cutoff and maximum oscillation frequencies are 29.7 and 58.8 GHz, respectively, for MOS-MHEMT. Also, the large-signal power gain, saturated output power, and maximum power-added efficiency at 2.4 GHz are 18.66 dB, 14.32 dBm, and 34%, respectively. The introduced liquid phase oxidation does not degrade the device radio-frequency performance, which is a good candidate for high speed applications. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3240876]