Fabrication of organic field-effect transistors based on phenyl-C61-butyric acid methyl ester (PCBM) with dielectric bilayers of silicon dioxide and a hydroxyl-free polymer buffer layer was carried out. A polymer buffer layer, which was made of either a cross-linked divinylsilane-bis-benzocyclobutene (BCB) polymer or a polystyrene-based dimethylchlorosilane monolayer (b-PS), turned out to be very smooth and hydrophobic. Cured BCB and two types of b-PS monolayers (M (n) = 8 and 108 kDa) covering SiO2 layers showed water contact angles of 91A degrees, 83A degrees, and 78A degrees and roughness less than a nanometer. Ascribed to favorable properties of insulating layers, high electron mobility values, ranging from 0.073 to 0.10 cm(2)/(V s), and a low threshold voltage (5.3-8.5 V) were obtained.