A method of improving the Al-bearing compound/GaAs interface against water vapor oxidation has been demonstrated. Amorphous native oxide formed by wet oxidation of an amorphous (Ga, As)/(Al, As) heterostructure on GaAs has exhibited an improved oxide/semiconductor interface with the incorporation of a thin GaP barrier layer of about two monolayers on the GaAs substrate. High resolution transmission electron microscopy shows an interfacial roughness on the order of 15 Å, and an enhancement of photoluminescence of three order of magnitude as compared to the as-grown counterpart without a GaP barrier indicates a great reduction in interface electronic traps. Having an improved interfacial roughness, a reduced interface trap density and an amorphous native oxide, this technique has a potential use in GaAs-based metal-oxide-semiconductor field-effect transistors. ©1998 American Institute of Physics.