The characteristics of thin-film transistors (TFTs) with pentacene active layers and source/drain contact layers consisting of either Au, Au coated with highly reduced graphene oxide (HRG), or plain HRG, are compared. It is shown that the incorporation of HRG as an interfacial material between gold source/drain contacts and pentacene in TFT devices results in improved electrical characteristics. The effect of the HRG layer is to improve the gold/pentacene interface leading to better charge injection, lower losses at the interface, and, consequently, higher effective carrier mobility.