The bias stress effect in pentacene thin-film transistors (TFTs) with and without MoOx interlayer was characterized. The device without MoOx interlayer showed a large threshold voltage shift of 5.1 V after stressing with a constant gate-source voltage of -40 V for 10000 s, while at the same condition, the device with MoOx interlayer showed a low threshold voltage shift of 1.9 V. The results can be attributed to the stable interface between MoOx/pentacene and small contact resistance change for the device with MoOx/Cu electrode. Pentacene-TFTs with MoOx interlayer showed a high field-effect mobility of 0.61 cm(2)/V s and excellent bias stability, which could be a significant step toward the commercialization of OTFT technology. (C) 2011 Elsevier B. V. All rights reserved.