The contact effect in bottom-contact pentacene-based thin-film transistor, with Au source/drain electrode, is investigated. By separating the voltage drop at the source contact from the source-drain voltage, the current-voltage characteristic of the injection contact is obtained. The contact characteristics are in good agreement with a model of carrier injection from a metal electrode into a disordered hopping system. (c) 2006 Elsevier B.V. All rights reserved.