Phase sensitive electrostatic force microscopy (EFM phase) investigations of semiconducting polymers, poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene) (178), are described, aimed at understanding the metal/polymer interfaces. The electrostatic behaviour and potential distributions of the Au/polymer/Au structure under various biases with emphasis on top and bottom Au contacts are presented. We observe, by analysing EFM phase data, that the top and bottom contacts of An can have drastic effects on the device performance. Moreover, differences in conductivity of conjugated polymers (P3HT > 178) are also reflected in EFM phase measurements, which correlate well with I-V measurements. Detailed analysis indicates that the influence of metal/film interfaces depends strongly on both the ability of charge transport properties of the organic films and the type of surface modification. (c) 2005 Elsevier B.V. All rights reserved.