states with a BE of 1118.4 eV and 1119.9 eV were measured for the emission from the GaInP and the GaOx, while on position 1 (pure GaAs), an asymmetric peak is visible and indicates GaAs at 1118 eV and a more oxidized compound at 1118.9 eV. This finding is in agreement with the two states observed for the As3d core level spectra, one centered at 41.4 eV and the other one centered at 3.1 eV higher in BE. The BE of the first state agrees with previous reports, and the energy difference between the Ga2p and the As3d core levels is 1076.6 eV as in a previous work. The relative energy difference of 3.1 eV between the two As3d core level states concludes the formation of As2O3 rather than As2O5. Valence band spectra were also recorded along the TCS (see Figure ). The energy differences of EF-EVB for the pure compounds GaAs and GaInP equal 1.4 eV and 0.4 eV, respectively. GaAs has a band gap of 1.4 eV and the one of GaInP equals 1.8 eV. It leads to a strongly n-type surface layer for the GaAs but, the EF-EVB difference of GaInP is in contradiction with the synthesized bulk that should be n-type. For the two III-V semiconductor devices that have been studied, the Fermi level position of the GaInP was modified. On the p-Ge substrate, the GaInP was synthesized p-doped but, after the TCS preparation, the Fermi level on the TCS surface appears to be shifted to the conduction band. On the n-GaAs substrate, the reverse is observed, the GaInP was synthesized n-doped but, after the TCS preparation, the Fermi level on the TCS surface appears to be shifted to the valence band. These deviations can be explained by the presence of the surface oxidation states that lead to Fermi level pinning, which prevents assigning properly the measured BE shifts to potential Fermi levels alignment that is expected at the junction between the bulks GaAs and GaInP.