The electrical characteristics of all-vacuum-processed pentacene thin-film transistors, with stable and reproducible performance, using high-throughput roll-to-roll processing have been demonstrated. The method allows a polymerized tripropyleneglycol diacrylate (TPGDA) insulator layer of thickness up to 1 μm to be obtained in a single pass by ultrahigh flash evaporation of a monomer onto a web travelling at 10 m·min-1and subsequent irradiation with an argon plasma emitted from a dc-sputtering cathode. The resulting organic thin-film transistors (OTFTs) exhibited field-effect mobility of 0.12 cm2 V-1·s-1, a threshold voltage of -21 V, a turn-on voltage of -2 V, and an on/off current ratio of 1 × 105. The effect of ambient air moisture on the device characteristics was investigated, showing that moisture has a reversible effect on the performance of the OTFTs exhibiting a shift in the turn-on voltage and deterioration in the on-off ratio. However, the effect was eliminated using a simple conventional encapsulation method. Our vacuum-based process thus demonstrates excellent potential for providing an alternative route to low-cost large-area organic electronics manufacturing.