The characteristics of InGaP/InGaAs metal-oxide-semiconductor (MOS) pseudomorphic high-electron-mobility transistor (PHEMT) with liquid phase-oxidized GaAs gate dielectric are demonstrated. Not only MOS-PHEMT has the advantages of the MOS structure, but also has high-carrier density, high-mobility 2DEG channel, and low surface state. The MOS-PHEMT exhibits larger transconductance, lower gate leakage current, higher breakdown voltage, higher cutoff frequency, and lower minimum noise figure compared with its referenced PHEMT counterpart. In addition, low-frequency flicker noise (1/f noise) is studied. MOS-PHEMT also exhibits better surface state and negligible generation-recombination noise, resulting in better 1/f noise. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.048112jes] All rights reserved.