A key issue in research into organic thin-film transistors (OTFTs) is low-voltage operation. In this study, we fabricated a pentacene thin-film transistor with an ultrathin layer of polyvinyl alcohol (9 nm) as a gate insulator, and obtained a device with excellent electrical characteristics at low operating voltages (below 2 V). This device was found to have a field-effect mobility of 1.1 cm2/V s, a threshold voltage of −0.98 V, an exceptionally low subthreshold slope of 180 mV/decade, and an on/off current ratio of 106. This favorable combination of properties means that such OTFTs can be operated successfully at voltages below 2 V.