We report on a single nanofiber field-effect transistor made from electrospun regioregular poly(3-hexylthiophene). Nanofibers, with diameters of 100-500 nm, were deposited by electrospinning from chloroform solution onto electrodes on a SiO2/Si substrate. The transistor exhibited a hole field-effect mobility of 0.03 cm(2)/V s in the saturation regime, and a current on/off ratio of 10(3) in the accumulation mode. Electrospinning offers a simple means of fabricating one-dimensional polymer transistors.