In the last years, conjugated polymers have received much attention in organic electronics for their use in the fabrication of low cost and flexible devices. As a result, different types of devices have been developed e.g. organic light emitting diodes (OLEDs), photovoltaic devices (OPVs) and field effect transistors (OFETs). For the OFETs in particular, their performance depends primarily on insulator/semiconductor interface, mainly due to charge carrier accumulation. Moreover, the interface properties strongly affect the charge transport through the device channel. For these reasons, the research for new semiconductor polymers and new dielectric materials is key to advancing the performance improvement of devices. In this work, the polymers PMMA, PVA, FORMVAR and PU were used as dielectric materials. Initially, parallel plate capacitors of the structure ITO/dielectric/A1 were made, in order to determine the dielectric constant of the insulators, get the curves JxV and the capacity per unit area. It was used to develop Top-Gate/Bottom-Contacts (TGBC) OFETs with structures of Au/P3HT/PMMA/Ag and Au/P3HT/PU/Ag. The thicknesses of the dielectric materials were varied to improve the performance of the devices. For the PMMA OFETs, the results obtained were concordant with those of the existing literature. The new PU OFETs presented with operating voltages of less than 5V, appropriate for applications of these OFETs in organic electronics. The mobility of the PU OFETs was 1.25cm(2)/V.s, the threshold voltage 0.02V and the On/Off ratio 100.