Even though the UP spectra reveal adsorbed OH groups at the surface, the Fermi level position within the bandgap, and with that the surface band bending, remain unaffected after the adsorption of water, indicating that not all dangling bond defects could be passivated by the OH groups. This also confirms that the P dangling bond center itself is not the active site for water dissociation. The dissociation of molecular water on InP surfaces requires free In sites as recently shown for Inrich InP(001) surface . For that reason, we suggest that water dissociation only occurs at step edges rather than on terraces of the P-rich InP(001) surface.