The characteristics of GaAs native oxides prepared by the liquid phase chemical-enhanced oxidation technique annealed at various ambiences including N2, O2, and mixture of N2 (85%) and H2 (15%) are investigated. The annealing temperatures range from 300 to 700 °C. The shrinkage of oxide film thickness, the increase of refractive index, the decrease of surface roughness, the enhancement of breakdown field strength and the reduction of leakage current have been obtained for all annealing conditions, except for annealing in the ambient atmosphere of N2 or O2 at temperature of 700 °C. It is found that annealed oxide films exhibited better thermal stability in an atmosphere of N2/H2 up to an annealing temperature of 700 °C. This is due to the existence of H atoms in the oxide films as demonstrated by SIMS depth profiles.