The effects of a vacuum seasoning process on poly (4-vinyl phenol) (PVP) gate dielectric for organic thin film transistors (OTFTs) with all soluble organic semiconductor were studied. A threshold voltage shift is usually seen when the organic gate insulator (OGI) is exposed to ambient air condition. This is because the OGI surface absorbs polar components such as oxygen and moisture. To overcome this environmental problem, we attempted to eliminate the polar components with heating during a high vacuum seasoning process of the PVP dielectric. To improve the performance and stability of OTFT devices, we studied the basic mechanisms of this high vacuum seasoning process on the PVP dielectric surface. The PVP-OTFTs exposed to heating during the high vacuum seasoning showed improved results in terms of a threshold voltage of -4.02 V and a field-effect mobility of 0.021 cm(2) V-1 s(-1) with a lower interface charge trap density of 6.62x10(-11) (cm(2) eV)(-1). All soluble OTFT processed by the high vacuum seasoning process presented much improved electrical characteristics in terms of lower threshold voltage, stiffer sub-threshold swings of just a few mV and near a zero turn-on voltage. (C) 2011 Elsevier B. V. All rights reserved.