It is generally well known that a semiconductor is a good photoanode if it is n-type (or a good photocathode if it is p-type). This means that in the case of a photoelectrochemical (PEC) system based on an n-type semiconductor like CdS, a photoeffect (i.e. photocurrent) can be observed only under anodic polarization. However, only occasionally have there been reports in the literature which have dealt with the observation of a cathodic photocurrent for n-type CdS electrodes. Studies have been performed on n-CdS electrodes possessing a low resistivity (and practically feeble photoconductivity) in connection with PEC solar cells. Quite interestingly, we have observed this photocathodic effect while carrying out PEC evaluation of semi-insulating (i.e. highly resistive) and highly photoconductive CdS electrodes doped with Cu and Cl (henceforth referred to as CdS + CuCl electrodes). The purpose of this paper is to investigate the origin of the photocathodic effect at such a CdS + CuCl based photoconductor/ electrolyte system. Results show that there is a close link between solid-state photosensitivity and PEC currents. This is particularly evident in the cathodic case, wherein the photocurrent, i.e. photomodulated majority carrier current, flows due to a reduction in Rs, the extent of which, in turn, is determined by the solid-state photosensitivity of the samples.