The electrical characteristics of double-oxide metal-oxide-semiconductor (MOS) structures on n-GaAs have been studied. The oxide layers were anodic and sputtered SiO2. The parameters analyzed were current conduction mechanism, resistivity, breakdown electric field, capacitance-voltage relationships and oxide fixed charges. Overall, the quality of this structure was inferior compared with the all-anodic oxide MOS structures. However, the parameters of the double-oxide MOS structure were considerably improved after rapid high temperature annealing. The sputter created damage; its removal and changes in the composite oxide structure after high temperature annealing were used to explain the observations.