Valence band x-ray photoelectron spectra (XPS) from oxide films grown on GaAs surfaces by thermal oxidation and electron cyclotron resonance (ECR) plasma oxidation are compared. The present work along with;previous studies clearly show that the ECR grown oxides are nearly stoichiometric and close to GaAsO4 while thermally grown oxides are closer to Ga2O3 having significant amounts of As+3 oxidation states. Metal oxide semiconductor.(MOS) structures were prepared by coating both the thermal and ECR plasma grown GaAs oxides with ECR plasma enhanced chemically vapor deposited (PECVD) SiO2 and then with evaporated Al as top contact. Interface charges in terms of fixed oxide charge and surface electronic states were obtained from conventional capacitance-voltage measurements. Despite the significant difference in the GaAs oxides structure, most notably the GaAsO4 like ECR plasma oxides, the interfaces prepared by both thermal and plasma oxidation were found to be equally unpassivated in terms of high levels of interface electronic states and Fermi level pinning.