A thin film transistor (TFT) has a gate electrode; a gate insulation layer, a semiconducting channel separated from the gate electrode by the gate insulation layer; a source electrode and a drain electrode. The gate insulation layer is a cross-linked cyanoethylated polyhydroxy polymer, e.g. a cross-linked cyanoethylated pullulan, having a high dielectric constant and the semiconducting channel has a network of semiconducting carbon nanotubes. The semiconducting channel is adhered to the gate insulation layer through a polymeric material. The carbon nanotubes adhere to the polymeric material and the polymeric material reacts or interacts with the gate insulation layer. TFTs have high mobilities while maintaining good on/off ratios.