An organic thin-film transistor and a method for manufacturing the same are described. The method forms a gate layer on a substrate, an insulator layer on the substrate, forming a semiconductor layer on the insulator layer, and a strip for defining a channel length on the semiconductor layer. An electrode layer is screen printed on the semiconductor layer, and a passivation layer is coated on the electrode layer. The organic thin-film transistor manufactured by the method of the invention has a substrate, a gate layer formed on the substrate, an insulator layer formed on the substrate, a semiconductor layer formed on the insulator layer, a strip for defining a channel length formed on the semiconductor layer, an electrode layer screen-printed on the semiconductor layer, and a passivation layer coated on the electrode layer. Thereby, an organic thin-film transistor with a top-contact/bottom-gate structure is obtained.