Using poly(3-hexylthiophene) (P3HT) covalently bonded with carbon nanotubes (CNT) as an active layer in a bottom-gate/top contact, Au/(P3HT)/(bilayer dielectric)/Si OTFT device has resulted in an enhanced charge transport. The CNTs were firstly functionalized via ligand exchange with ferrocene, next lithiated by sec-butyllithium (s-BuLi) and then linked anionically with P3HT which has been synthesized via the modified Grignard metathesis method. Compared to the pristine P3HT, the CNTs-containing P3HT composite material has a higher energy level of HOMO and a smaller electrochemical bandgap E(g)(chem). The smaller bandgap enhances the charge carrier transport and the higher HOMO energy level indicates a reduced barrier and an increased injection rate for charge carriers at the source contact. Furthermore, the threshold voltage V(T) of CNTs-containing P3HT samples is lower and its saturation current I(D) and the the field-effect mobility are higher. An OTFT device fabricated with such a composite sample containing 1.16% CNTs has a carrier mobility and saturation current three to five times higher than pristine P3HT.