A thin film of polymethylmetacrylate (PMMA) acting as a buffer layer has been employed in order to fabricate high-quality pentacene thin-film transistors (TFTs), both in bottom contact and top contact configuration. A PMMA buffer layer allows to reduce the interaction between a π-conjugated system of pentacene and the metal or dielectric substrate. We show that a thin PMMA buffer layer improves crystal quality along the metal contacts’ boundaries, while still allowing good ohmic contact. Pentacene TFTs, including a PMMA buffer layer, show very high field-effect mobility, μFE=0.65 and 1.4cm2∕Vs, for bottom and top contact configuration, respectively, and remarkable steep subthreshold region.