Dielectric spectroscopy has been used to extract the AC and DC electrical conductivities of P3MT complexed with the paramagnetic ion Fe2+, and these were compared to data for uncomplexed P3MT in the frequency range of 1 Hz-10 MHz. The polymers were nominally undoped; however, the presence of residual Fe2+ ions from the polymerisation reaction renders the materials p-type semiconductors. Measurements were carried out over the temperature range 123-323 K. An analysis of the frequency-dependent complex conductivity together with the DC conductivity can be used to elucidate whether free charge conduction, charge hopping or quantum tunnelling is the dominant conduction mechanism. The results were compared to the predictions of a variety of theoretical conduction models. It was found that the presence of the Fe2+ ions produced greater long-range order at low temperatures by complexing between the sulphur heteroatoms of four 3-methylthiophene monomer units. This provided an additional barrier hopping conduction mechanism at low temperatures (183-243 K), and the hopping occurred over a barrier height within the range 0.45-0.6 eV. Crown Copyright (C) 2002 Published by Elsevier Science Ltd. All rights reserved.