Field- effect transistors ( FETs) based on dihexylsexithiophene ( DH6T) films were prepared on a SiO2/Si substrate with asymmetric gold source and aluminum drain electrodes. DH6T grew in layer- by- layer manner on SiO2 with its molecular axis perpendicular to the surface. Visible light emission from the channel region was observed as the gate and drain voltage increased, and the emission spectra varied depending upon the layer thickness.