The Fermi level at the Ga oxide/GaAs interface has been unpinned by rf plasma cleaning the GaAs surface in H2 and N2. Following plasma cleaning, a Ga oxide film is reactively electron beam deposited onto the substrate. Metal-oxide-semiconductor (MOS) capacitors fabricated on these structures show good high-frequency capacitance-voltage characteristics. This indicates that the density of interface states has been reduced to ∼10 11 eV-1 cm-2. The MOS capacitors are found to be stable in air after several months.