The photoelectrochemical properties of nanocrystalline In2O3 film electrodes prepared by sol-gel method have been studied. The surface and bulk characterization of sol-gel-derived In2O3 films and powders heated at different temperatures has been performed using X-ray diffraction analysis, X-ray photoelectron, IR-absorption and photoelectrochemical spectroscopies. A significant shift of the photocurrent onset potential in the positive direction and a rise in the photocurrent quantum yield are observed as the temperature of the electrode heat treatment increases from 200 to 400 degrees C. A tentative explanation for this effect has been provided, taking into account the formation of the finest hydroxide layer at the nanocrystallite surface of slightly heated In2O3 films. (C) 2000 Elsevier Science Ltd. All rights reserved.