The ambipolar characteristics of polyaniline-poly(styrene sulfonic acid) (PANI-PSS)-based organic thin film transistor (OTFT) via poly(vinyl alcohol) surface modification were demonstrated. Through ion-assisted electrochemical doping, the PANI-PSS-based OTFT shows the unobvious ambipolar operation caused by the incompatibility interface between water-soluble PANI-PSS and poly(4-vinylphenol) dielectrics. With appropriate control of the interface conditions, the ambipolar characteristics of OTFTs can be enhanced significantly. Hole mobility can be increased from 0.65 to 3.36 cm(2)/V s while electron mobility is at 1.19 cm(2)/V s. (C) 2012 Elsevier Ltd. All rights reserved.