Since the electrochemical reaction at electrodes of PEMFC is a form of exothermic reaction, three-dimensional non-isothermal numerical simulation was developed including the energy equation with all heat source terms such as reversible heat generation and irreversible heat release attributed to ohmic and activation polarization. The results show that the maximum temperature is observed at the cathode because of reaction heat from water formation reaction and temperature at the electrolyte along channel increases due to accumulative heat addition and heat is mainly generated by irreversible loss at a low voltage and by water formation loss at a low current density. (C) 2007 Elsevier B.V All rights reserved.