The substitution of selenium by sulphur in thin film solar cells still is a challenging topic. The origin of the related disadvantageous electrical proper ties to date is not well understood. A distinction of effects caused by preparation technology and intrinsic material properties is difficult. Therefore, comparative studies on bulk single crystals should provide valuable information. We grew CuIn(SxSe1 x)(2) crystals by the solution Bridgman method using CuSe as a solvent. The crystals were analysed by x-ray diffraction, photoluminescence and Hall-effect measurements and turned out to be of an excellent electrical homogeneity. The temperature dependent carrier concentrations can be well explained by assuming a two acceptor and one donor model. The activation energies of the acceptor levels clearly shift to higher values when selenium is substituted by sulphur. This is confirmed by photoluminescence measurements, which reveal an acceptor to band edge transition shifting to higher energies with increasing sulphur content.