Potential profiles of an Al/poly(3-hexylthiophene), PHT film/Au diode through Al to Au electrodes have been measured directly using a micro-manipulator with a potential probe tip. A steep potential cliff is observed at the interface of Al/PHT for negative biases to An against Al, indicating the existence of a depletion layer with higher resistance than that of the PHT bulk region. For a positive bias above +1 V to An, the interface resistance at Al/PHT decreases markedly, resulting in a forward current in the rectification diode. It is found that the contact resistance of PHT/Au is unexpectedly large in spite of the ohmic behavior. The effect of light on the depletion layer is also studied. It is stressed that the contact resistances of PHT and metals are significantly important and determine the performance of organic electronic devices. (C) 2003 Elsevier B.V. All rights reserved.