Mobilities of positive charge carriers in poly(3-hexylthiophene) (PHT) films of 54%, 70%, 81%, and 97% in regio-regularity were electrochemically measured over a range of doping levels. The results show that better ordered stacking structures enhance mobilities, but affect little features of the mobility change by doping. The common doping level of ca. 1% for the onset of the drastic mobility increase implies that the pi-pi stacking structures facilitating a charge transport in neutral or lightly doped PHT films are not responsible for the evolution of metallic conduction in PHT films. (C) 2002 Elsevier Science B.V. All rights reserved.