A study of the oxidation of n-InP in pH 5.0 aqueous media was undertaken to confirm the formation of InPO4 in the negative potential region. The study necessitated the use of the two buffers, acetate and phosphate, in order to demonstrate phosphate formation. In order to interpret the voltammograms and XPS results of the n-InP systems, passivation studies of metallic indium were performed in the same buffer systems. Voltammetry and XPS results of indium and n-InP in acetate buffer systems depicted the formation of InPO4 (and/or In(PO3)(3)) on InP. Similar studies in phosphate buffers showed that n-InP does not undergo oxidation to the phosphate species. AFM images of polarized n-InP indicated that the formation of InPO4 (In(PO3)(3)) in acetate buffer is due to the oxidation of the exposed InP on the surface of the n-InP electrodes. The polarized n-InP surfaces in phosphate buffer were completely covered with metallic indium. The surface of n-InP after successive voltammograms in acetate buffer contained a large amount of In(OH)(3) and was accompanied with greater amounts of phosphate species closer to the interface.