Organic thin film transistors with C_(60) as an n-type semiconductor have been fabricated.A tantalum pentoxide(Ta_2O_5)/poly-methylmethacrylate(PMMA) double-layer structured gate dielectric was used.The Ta_2O_5 layer was prepared by using a simple solution-based and economical anodization technique.Our results demonstrate that double gate insulators can combine the advantage of Ta_2O_5 with high dielectric constant and polymer insulator for a better interface with the organic semiconductor.The performance of the device can be improved obviously with double gate insulators,compared to that obtained by using a single Ta_2O_5 or PMMA insulator.Then,a good performance n-type OTFT,which can work at 10 V with mobility,threshold voltage and on/off current ratio of, respectively,0.26 cm~2/(V·s),3.2 V and 8.31×10~4,was obtained.Moreover,such an OTFT shows a negligible“hysteresis effect”contributing to the hydroxyl-free insulator surface. Organic thin film transistors with C_ (60) as an n-type semiconductor have been fabricated. A tantalum pentoxide (Ta_2O_5) / poly-methylmethacrylate (PMMA) double-layer structured gate dielectric was used. The Ta_2O_5 layer was prepared by using a simple solution-based and economical anodization technique. Our results demonstrate that double gate insulators can combine the advantage of Ta_2O_5 with high dielectric constant and polymer insulator for a better interface with the organic semiconductor. The performance of the device can be improved obviously with double gate insulators , compared to that obtained by using a single Ta 2 O 5 or PMMA insulator.Then, a good performance n-type OTFT, which can work at 10 V with mobility, threshold voltage and on / off current ratio of, respectively, 0.26 cm 2 / (V · s), 3.2 V and 8.31 × 10 -4, was obtained. Moreover, such an OTFT shows a negligible “hysteresis effect” contributing to the hydroxyl-free insulator surface.