Cuprous oxide has been prepared by the photoelectrochemical reduction of a CuO film formed on a conducting substrate by the anodic deposition from an alkaline solution of a Cu(II)-amino acid complex. Both copper oxide films thus prepared are found to be typical p-type semiconductors. The onset of the cathodic photocurrent due to the reduction of O-2 on CuO/ITO (ITO, indium tin oxide) and Cu2O/ITO electrodes give positive shifts of about 0.2 and 0.03 V, respectively, from the dark current rises. Optical bandgap energies of CuO films depend on the amino acids used, 1.56 (glycine), 1.40 (alanine), 1.38 (isoleucine), 1.38 eV (valine), and the value of E-g for the Cu2O film is 2.17 eV. The relationship between the flatband potential (V-FB) and the pH for CuO and Cu2O films are both linear with the slope of about -60 mV/pH in agreement with the Nernstian expression for the V-FB of a semiconductor. (C) 2004 The Electrochemical Society.