Semiconducting thin films of n-CdSe were electrochemically deposited on Ti substrates with the potential difference as the driving force. By using a photomasking technique different film thicknesses could be obtained on the same substrate. The film electrodes were characterized with photoelectrochemical (PEG) imaging, optical microscopy and scanning electron microscopy (SEM)/energy-dispersive X-ray analysis. PEC imaging is done with a fibre-optical laser scan microscope that allows a laterally resolved mapping of the photoelectrochemical response. The results show that substrate preparation is crucial for the photoelectrochemical performance of the film. At scratches in the substrate the film shows a lower photoresponse. Very thin films give low photoresponse. These films also show a different morphology in the SEM pictures. The films are not homogeneous and have a less ideal composition when they are too thin. We have found PEC imaging a good complement to other methods for characterization of semiconducting thin films.