We report on the low-voltage-driven organic thin-film transistors (OTFTs) with various organic films [pentacene, tetracene, and copper-phthalocyanine (CuPc)] for the semiconductor channel on a thin poly-4-vinylphenol (PVP)/aluminum oxide (AlOx) bilayer gate dielectric. Quite a large capacitance of 31 nF/cm(2) and a high dielectric strength of similar to 4 MV/cm were achieved from the 45 nm thin polymer/100 nm thick A1O(x) bilayer dielectric. All the organic channel layers deposited on the bilayer exhibited good crystalline quality as characterized by both X-ray diffraction (XRD) and atomic force microscopy (AFM) surface imaging because the bilayer had a smoothened and hydrophobic PVP surface on top. Our OTFTs with the bilayer dielectric exhibited good field-effect mobilities of 0.55, 0.07, and 0.004 cm(2)/V s for pentacene, tetracene, and CuPc channels, respectively, at a low operating voltage of less than -8 V. (c) 2007 The Electrochemical Society.