Electrical properties of three kinds of poly(methyl methacrylate) (PMMA) with different tacticity, i.e. isotactic(i), syndiotactic(s), and atatic(a), were investigated for the application in field effect transistor. Metal-insulator-silicon structures were fabricated via spin coating PMMA on heavily doped p-type silicon (p(+)-Si) followed by evaporating gold electrode. The electrical characteristics were remarkably improved by heat-treatment at temperatures 40 K above glass transition temperatures of PMMAs. Among the three PMMA isomers, i-PMMA was observed to possess the highest dielectric strength (1.1 MV/cm) with the lowest leakage current density, but also the lowest dielectric constant (k=2.5). Top-contact thin film transistors fabricated with the configuration of NiOx/pentacenc/i-PMMA/p(+)-Si, where the NiOx being used as a source/drain electrode, displayed relatively a decent field effect mobility of 0.042 cm(2)/V-s which is not that low with such a low dielectric capacitor as thick i-PMMA film. (c) 2006 Elsevier B.V. All rights reserved.