Top-contact organic field-effect transistors based on poly(3-hexylthiophene) (P3HT) active layer were fabricated using gate dielectric (SiO(2)) modified with 3-amino propyltrimethoxysilane (APTMS) multilayers. It has been demonstrated that the treatment of dielectric with APTMS enhances the field-effect mobility as well as the on/off ratio of the devices by nearly two orders of magnitude. This is attributed to conformational changes as well as to an improved uniformity of the spin coat P3HT films on the APTMS-modified substrate as revealed by atomic force microscopy, Fourier transform infrared spectroscopy and UV-Vis measurements. (C) 2009 Elsevier B.V. All rights reserved.