The efficiency of photoelectrochemical cells with thin‐film electrodes can be enhanced by illuminating the semiconductor electrode in salt solution under closed‐circuit condition. The photoactivation mechanism involves the photooxidation of to elemental selenium with concomitant release of cadmium ions into the salt solution and subsequent reductive dissolution of the resulting layer of elemental selenium. This method can be controlled more precisely than acid etching and hence is more suitable for large scale application.