In this study, the authors used a double-layer gate dielectric with the same solution processable polyimide to form a gate insulator gate layer after hard curing at 200 C to improve the roughness of surface of the nanocomposite gate dielectric with high dielectric constant. The bottom layer is a nanocomposite with polyimide and nanoparticle TIO2 blending, which is responsible for enhancing the dielectric constant of the gate insulator. The upper layer is the neat polyimide, which is responsible for smoothing the roughness of the gate insulator and contacting with semiconductor (pentacene) in this work. An organic thin-film transistor device made from the double-layer nanocomposite gate dielectric exhibits very promising performance, including high current on-to-off ratio of about 6 x 10(5), threshold voltage of -10 V, and moderately high field mobility of 0.15 cm(2) V-1 s(-1). (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3093881]