High-performance pentacene field-effect transistors have been fabricated using Al2O3 as a gate dielectric material grown by atomic layer deposition (ALD). Hole mobility values of 1.5 +/- 0.2 cm(2)/V s and 0.9 +/- 0.1 cm(2)/V s were obtained when using heavily n-doped silicon (n(+)-Si) and ITO-coated glass as gate electrodes, respectively. These transistors were operated in enhancement mode with a zero turn-on voltage and exhibited a low threshold voltage (< -10V) as well as a low sub-threshold slope (< 1 V/decade) and an on/off current ratio larger than 10(6). Atomic force microscopy (AFM) images of pentacene films on Al2O3 treated with octadecyltrichlorosilane (OTS) revealed well-ordered island formation, and X-ray diffraction patterns showed characteristics of a "thin film" phase. Low surface trap density and high capacitance density of Al2O3 gate insulators also contributed to the high performance of pentacene field-effect transistors. (c) 2007 Elsevier B.V. All rights reserved.