It is shown that the native oxide of GaAs can be thermally grown easily at a temperature of 250°C using a high-pressure oxidation technique. The resulting oxide films are uniform, chemically stable and have a breakdown strength of 68 x 106 V/cm and a bandgap energy greater than 6.5 eV. The chemical composition of the oxide films is studied using X-ray photoelectron spectroscopy, and it is found to contain oxides of both gallium and arsenic. © 1987, The Institution of Electrical Engineers. All rights reserved.