The long-term stability of pentacene thin-film transistors (TFrs) encapsulated with a transparent SnO2 thin-film prepared by ion beam-assisted deposition (IBAD) was investigated. After encapsulation process, our organic thin-film transistors (OTFTs) showed somewhat degraded field-effect mobility of 0.5 cm(2)/(V s) that was initially 0.62 cm(2)/(V s), when a buffer layer of thermally evaporated 100 nm SnO2 film had been deposited prior to IBAD process. However, the mobility was surprisingly sustained up to 1 month and then gradually degraded down to 0.35 cm2/(V s) which was still three times higher than that of the OTFT without any encapsulation layer after 100 days in air ambient. The encapsulated OTFTs also exhibited superior on/off current ratio of over 10(5) to that of the unprotected devices (similar to 10(4)) which was reduced from similar to 10(6) before aging. Therefore, the enhanced long-term stability of our encapsulated OTFTs should be attributed to well protection of permeation of H2O and O-2 into the devices by the IBAD SnO2 thin-film which could be used as an effective inorganic gas barrier for transparent organic electronic devices. (c) 2005 Elsevier B.V. All rights reserved.