The carrier mobility of pentacene OTFT is enhanced by annealing its gate dielectric (SiO2) in NH3. The device has a field-effect mobility of 0.53 Cm-2/V s, with on/off current ratio of 1 06, and subthreshold slope of 2.4 V per decade. When compared with the control sample with N-2-annealed SiO2 as gate dielectric, the mobility of the proposed pentacene OTFT is increased by over 50%. AFM micrographs show that the higher mobility should be due to the smoother gate-dielectric surface passivated by the NH3 annealing, and also larger pentacene grains grown on the smoother gate-dielectric surface. (c) 2006 Elsevier Ltd. All rights reserved.