Pentacene thin-film transistors(TFTS) were fabricated on glass substrates. Aluminum andgold were used for gale and source/drain electrodes. Silicon dioxide was deposited as a gate insulator by PECVD and patterned by reactive ion etching(RIE). The semiconducting pentacene layer was thermally evaporated in vacuum at a pressure of about 10(-8) Torr and a deposition rate of 0.3 Angstrom /sec. The fabricated devices exhibited the field-effect mobility as large as 0.07 cm(2)/V sec, threshold voltage as low as -3.3V, and the on/off current ratio larger than 10(7).