A prototypical semiconducting bicomponent system consisting of a conjugated polymer, that is, poly(3-hexylthiophene) (P3HT), blended with a small thiophene containing conjugated molecule, that is, an alkyl-substituted bisphenyl-bithiophene [phenylenethiophenethiophenephenylene (PTTP)], has been used as an electroactive active layer in field-effect transistors (FETs). The self-assembly of this bicomponent system at surfaces has been studied at different length scales, from the nanoscale to the macroscale, and compared with the behavior of monocomponent films of PTTP and P3HT. The correlation between morphology and electric properties of the semiconducting material is explored by fabricating prototypes of FETs varying the relative concentrations of the two-component blend. The maximum charge carrier mobility value, achieved with a few percent of PTTP component, is not simply due to a uniform dispersion of the molecules in the polymer matrix, but rather to the generation of very long percolation paths, whose composition and electrical properties can be tuned with the PTTP concentration. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012