Oxotitanium phthalocyanine (TiOPc)-based organic thin-film transistors (OTFTs) were fabricated by introducing para-sexiphenyl (p-6P) thin-film as the modified layer of gate insulator. The typical ambipolar transport behavior may be observed in ambient, which exhibited a balanced charge transport with a hole mobility of 8 x 10(-2) and an electron mobility of 3 x 10(-2) cm(2)/V.s. More importantly, the on/off ratio for both n- and p-type accumulation-mode has reached 10(4) and simultaneously exhibited good air-stability. Furthermore, capacitance-voltage characteristics were presented in order to further clarify the operation procedures of two kinds of charge-carriers. The excellent ambipolar transport behavior is attributed to the surface modification properties of p-6P for better electron transport and highly ordered thin-film morphology of TiOPc. These results demonstrate that the surface characteristics of insulator play a crucial role in realizing ambipolar devices. (C) 2017 Published by Elsevier B.V.