The thermodynamic analysis of photoelectrochemical (PEC) hydrogen production is performed in this work for air mass 1.5 solar insolation. Because the energy required for splitting water decreases as temperature is increased, heating the system by using the long wavelength energy will increase the system efficiency. As the energy band gap of the photoelectrode increases, the induced photo-current is decreased. If photons absorbed are all excited, the maximum photo-current is 63.8 mA/cm(2). For TiO(2) (similar to 3.2 eV) and Fe(2)O(3) (similar to 2.1 eV), the maximum photo-current is respectively 0.68 mA/cm(2) and 10.4 mA/cm(2). The maximum power conversion efficiency of a PEC cell is 44.1%. For TiO(2) and Fe(2)O(3), the power conversion efficiency is 2.8% and 21.9%, respectively. At 647 K and quantum efficiency = 30%, the maximum hydrogen production rate is 7.5 L/m(2) h and 41.8 L/m(2) h for TiO(2) and Fe(2)O(3), and the maximum efficiency of solar to hydrogen is 2.71% and 14.2% for TiO(2) and Fe(2)O(3) respectively. In order to increase the maximum hydrogen production rate, it is more effective to raise the quantum efficiency than raising the reaction temperature. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.