The surface onto which polymeric semiconductors are cast from solution plays an important role in determining the electrical transport properties of the polymeric thin film. The authors use synchrotron-based x-ray diffraction to show that even moderate roughness (rms similar to 5 angstrom) can affect the texture of semicrystalline poly(thiophene) thin films. Moreover, the authors use a novel optical characterization technique (surface plasmon resonance spectroscopy) to characterize the appearance of electronic states in the bandgap of thin films (similar to 20 nm) of regioregular poly(thiophene). Such states may be due to the heterointerface between the thin Au substrate and the polymer. (C) 2008 American Vacuum Society.