A flexible organic field effect transistor was developed based on 2,5-dihexylsexithiophene (DH6T), a recently synthesized thiophene oligomer with high regioregularity. The oligomer was tested on highly doped silicon as gate electrode and SiO2 as gate insulator film. For experiments on flexible substrates, aluminium was used as gate electrode. Several materials were tested as gate insulators with the best dielectric properties obtained for anodically formed aluminium oxide. In combination with the oligomer, this gate insulator is definitely suitable for further developments. (C) 2004 Elsevier Ltd. All rights reserved.