The effects of operating temperature and thickness of gate dielectric on the electrical characteristics of a GaAs MOSFET have been investigated. We fabricated the GaAs MOSFET using Ga2O3(As2O3) as the gate dielectric prepared by a liquid-phase chemically enhanced oxidation method. By reducing the temperature from 150 degreesC to -50 degreesC, the transconductance call be enhanced about 100% for a 1 mum gate-length MOSFET with oxide thickness of 35 nm. An increasing trend of transconductance can also be observed by reducing the gate-oxide thickness. In addition, the short-circuit current gain cutoff frequency f(T) and the maximum oscillation frequency f(max) as a function of temperature and gate-oxide thickness are discussed for different values of gate length.