We propose a viable method of improving the storage stability of pentacene organic thin-film transistors (OTFTs) by the formation of polyimide (PI) passivation layer on the top of OTFTs. Solution-processed passivation layers can degrade the performance of OTFTs owing to fatal damage caused by chemical solvents on organic semiconductors. In this study, the vapor deposition polymerization method, which is in situ dry process, is introduced to fabricate a patterned PI passivation layer. It is shown that the presented PI passivation layer is effective for protecting moisture in ambient air and the characteristic variation of OTFT is almost negligible even after the passivation process. Under an average relative humidity of 50% at room temperature, the OTFT with such a PI passivation layer exhibits an extended half-life time of about 360 h in its switching behavior, while less than 24 h for the device without any passivation layer. (C) 2010 Elsevier Ltd. All rights reserved.