Contact effects have been analyzed in fully printed p-channel OTFTs based on a pentacene derivative as organic semiconductor and with Au source–drain contacts. In these devices, contact effects lead to an apparent decrease of the field effect mobility with decreasing L and to a failure of the gradual channel approximation (GCA) in reproducing the output characteristics. Experimental data have been reproduced by two-dimensional numerical simulations that included a Schottky barrier (Φb=0.46eV) at both source and drain contacts and the effects of field-induced barrier lowering. The barrier lowering was found to be controlled by the Schottky effect for an electric field E