The application of surface science techniques to investigate elementary processes in photoelectrochemistry is shown based on a number of experiments performed during the last years. For these experiments, layered chalcogenide WSe2(0 0 0 1) van der Waals, surfaces are used as semiconductor substrates as they provide ideal surface properties for fundamental studies. After a short introduction to the experimental techniques, we will present results of adsorption and coadsorption experiments performed to investigate different aspects of semiconductor/electrolyte contacts. For H2O and Br-2 adsorbed as single species and coadsorbed with each other, the electronic states involved in contact formation can be identified and different mechanisms of interface interaction have been deduced. Na and H2O coadsorption experiments give information about solute solvent interaction as, e.g. solvation energies. Finally, a complex electrolyte phase containing all relevant species has been prepared by coadsorbing Br-2, Na and H2O. (C) 2004 Elsevier B.V. All rights reserved.