Growth and properties of cadmium selenide semiconductor thin films prepared by a new electrochemical selenization process (ECS) are described. The as-formed CdSe thin films have large (similar to 1 mu m) crystallites in hexagonal modification. The differential selenization kinetics in the intra- and intergrain regions causes the formation of stoichiometric CdSe film to be highly dependent on time. CdSe composition is independent of selenization parameters. Two direct optical band gaps at 2.09 and 1.44 eV, as opposed to a single gap at 1.7 eV, are observed in CdSe film selenized at 0.6 and 0.4 mA/cm(2) current densities, respectively. A mechanism of selenization based on Cd ionization by oxygen reduction and reaction with cathodically released Se ions is proposed for the CdSe film formation.