The temperature dependence of the built-in voltage of organic semiconductor devices is studied. The results are interpreted using a simple analytical model for the band bending at the electrodes. It is based on the notion that, even at zero current, diffusion may cause a significant charge density in the entire device, and hence a temperature dependent band bending. Both magnitude and temperature dependence of the built-in potential of various devices are consistently described by the model, as the effects of a thin LiF layer between cathode and active layer. (c) 2006 American Institute of Physics.