The integrated device of the organic field transistor (OFET) based on alpha,omega-dihexylsexithiophene and the organic light emitting diode (OLED) was fabricated on the same indium tin oxide (ITO)-coated glass substrate by using the photoresist gate insulator with an average surface roughness of 0.2 nm. OFET has a top contact structure with the Au source and drain electrodes. The current and luminance of an OLED were controlled by varying the gate voltage. The field effect mobility of the OFET with non-treated photoresist gate insulator increases with increasing the substrate temperature and is obtained up to about 0.1 cm(2)/V s at a substrate temperature of 90 degrees C, while the devices with octadecyltrichlorosilane (OTS)-treated gate insulator are almost independent of the substrate temperature and have up to about 0.1 cm (2)/V s at the substrate temperature region from 20 degrees C to 90 degrees C. The OTS-treated OFET at 60 degrees C has a highest carrier mobility of 0.137 cm(2)/V s and a current on/off ratio of 10(5). The OTS treated gate insulator obviously plays an important role in improving the performance of the OFETs. Current in the order of more than 0.1 mu A flows from the semitransparent top contact type OFET utilizing the sputter deposited amorphous carbon nitride/ITO bilayer instead of Au electrode as the source and drain electrodes. (c) 2005 Elsevier B.V. All rights reserved.