We investigate the effect of the thermal treatment on the reduction of the trap density (N-it) at the organic-organic interface together with the mobility dependency to the gate-bias in an organic thin-film transistor (OTFT). The Nit between a poly(4-vinylphenol) layer and a pentacene film is found to be reduced due to the rearranged pentacene molecules during thermal treatment and the resultant mobility is obtained as high as 1.78 cm(2)/V s. In addition, the mobility dependency to the gate-bias is decreased at the case of thermally-treated OTFT. It can be concluded that the N-it plays an important role on the electrical performances as well as the bias-stability. (c) 012 Elsevier Ltd. All rights reserved.