Nanocrystalline sulfur-doped cadmium sulfide (CdS) prepared by microwave synthesis was investigated. Photoelectrochemical and optical characteristics of sulfur-doped CdS exhibit the photoelectrochemical photocurrent switching effect. Depending on the wavelength and applied bias, the anodic and/or cathodic photocurrent was observed. The unusual behaviour of nanocrystalline CdS allowed the construction of a combinatorial logic system from this material.