The photoelectrochemical reduction of carbon dioxide (CO2) at p-type semiconductor electrodes, p-GaAs and p-InP, was studied in the methanol-based electrolyte. The main products from CO2 were carbon monoxide and formic acid. The onset potentials of the photocathodic current in the methanol-based electrolyte were around -1.2 and -0.8 V versus Ag/AgCl (saturated KCl) with p-GaAs and p-InP electrodes, respectively. Since the onset photopotentials were more positive compared to those with normal metallic electrodes, the photo-aided electrolysis can save electrical energy corresponding to a potential shift of 0.3-1.0 V to less negative potentials. The maximum current efficiency for CO (r(f) = 41.5%) was obtained at -2.4 V for the p-InP photocathode. The current efficiencies for CO were better relative to those for formic acid at both p-GaAs and p-InP electrodes. The p-type indium phosphide electrode was found to be more effective than p-Si and p-GaAs for the photoelectrochemical reduction of CO2 in methanol-based electrolyte. (c) 2005 Elsevier B.V. All rights reserved.