The X.P.S. measurements permit the obtention of the structure of the native oxide with etching procedures. The modification of the surface stoechiometry has been studied in presence of water, oxidizing species and sulfur. The modification by immersion in aqueous electrolytes of the native oxide films has been followed by X.P.S. according to specific procedures. The difference of surface reactivities of InP and GaAs has been once more evidenced. The typical reactivity of phosphorus element is evidenced in the interaction Ce-P and the specific reactivity of In is proved during the sulfuration of InP. Only a coupling between X.P.S. and Electrochemical techniques permit to obtain sufficient information during the deposition and the chemical transformation of thin oxide, insulator or metallic film on the semiconductor surface during the fabrication of complex microscopic electronic devices.