In this work, pentacene based thin film transistors (TFTs) with different channel lengths (L¿=¿2.5, 5, 10 and 20¿µm) have been fabricated and characterized electrically. Exploiting the electrical characteristics, we have analyzed the channel length effect on the key parameters of fabricated TFTs. We found that the performance of pentacene-TFTs was enormously enhanced by the reduction of channel length .We have also examined the influence of contact and channel resistances (RC and Rch) on the electrical proprieties of fabricated TFTs, using the transmission line method (TLM). Then, we have modeled the dependence of the total resistance RT on the gate voltage VG using the grain boundary trapping Meyer–Neldel rule (GBT-MNR) model and we have successfully reproduced, the output characteristic of pentacene TFTs using the overall resistance extracted from the GBT-MNR model. Finally, in order to investigate the channel length effect on the dynamic behavior of fabricated devices, we have reported a dynamic model based on the quasistatic assumptions which were used for metal-oxide-semiconductor field-effect transistor (MOSFET). Accordingly, we have presented a simple small-signal equivalent circuit to calculate theoretically the capacitances of pentacene-TFTs for different channel lengths.