Anodically oxidized layers were grown on GaP (111) surfaces from a solution of N‐methyl acetamide, H2O, NH4OH, and citric acid having apH value of 9.0. The layer growth rate was 11 A˚/V with a constant current density of 0.5 mA/cm2. Auger electron spectra and depth profiles of the components were measured. The phosphorousL3M2,3M2,3transition at 117 eV suffered a chemical shift in the oxide layers, and the shape of the first derivative of the Auger signal was completely different from that observed with P in GaP. Observation of the phosphorousKL2,3L2,3transition at 1858 eV indicated that the ratio of P/Ga had a constant value throughout the oxide layers. Only the oxygen concentrations varied along with the depth.