Impedance and current-voltage spectral measurements have been carried out on the Au/poly(3-pentylthiophene)/Au sandwich system in which the polymer was in the form of a pressed powder. The device shows an ohmic dc resistance. The specific conductivity of the material was in the range of insulators. The investigated sandwich system displays a relationship between the specific conductivity and the polymer thickness which is characteristic for molecular-scale disordered materials. Modification of the polymer by gaseous ozone in relatively high concentration causes a significant increase of the specific conductivity. Ozone treatment leads to p-doping of the polymer resulting in a temporary increase in conductivity as well as a modification of the morphology; the latter is stable and results in a permanent increase of the sample conductivity. (C) 2011 Elsevier B.V. All rights reserved.