We fabricated a photovoltaic water electrolysis device in which whole electrolyzing parts were formed on one chip. This was made by attaching the Co-Mo and the Fe-Ni-O electrodes for hydrogen and oxygen evolution, respectively, on the a-Si solar cell. Water electrolysis could be conducted simply by dipping and irradiating the device in electrolyte. The device was durable for more than 18 h electrolysis by irradiation in the KOH electrolyte,at pH 13 at a conversion efficiency from solar to hydrogen energy of 2.5%. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.