The characteristics of GaAs native oxides prepared by the liquid phase chemical-enhanced oxidation technique annealed at various ambiences including N-2, O-2, and mixture of N-2 (85%) and H-2 (15%) are investigated. The annealing temperatures range from 300 to 700 degreesC. 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 N-2 or O-2 at temperature of 700 degreesC. It is found that annealed oxide films exhibited better thermal stability in an atmosphere of N-2/H-2 up to an annealing temperature of 700 degreesC. This is due to the existence of H atoms in the oxide films as demonstrated by SIMS depth profiles. (C) 2004 Elsevier Ltd. All rights reserved.