Sintered Bi2O3 pellets exhibited insulating properties at room temperature. Partial reduction of sintered Bi2O3 pellets increased the conductivity. Reduced Bi2O3 pellets exhibited n-type semiconductor properties. Microcrystals of Bi2S3 were formed on sintered Bi2O3 pellets by sulfurizing them in H,S atmosphere. The direct band-gap and indirect band-gap of Bi2S3 were evaluated as 1.2 and 0.4eV, respectively. A high incident photon to current conversion efficiency in the near IR region was observed on Bi2S3 Bi2O3 electrodes. Photocurrent generation of Bi2S3\Bi2O3 electrodes was explained from the viewpoint of semiconductor sensitization. The flat band potential of Bi2S3 was evaluated as -1.1 V vs. Ag1AgCl in aqueous polysulfide redox electrolyte (1 M OH-, 1 M S2-, 10(-2) M S). (C) 2002 Elsevier Science B.V. All rights reserved.