Pentacene thin-film transistors (TFTs) encapsulated with a transparent SnO2 thin-film prepared by ion-beam-assisted deposition (IBAD) were fabricated. We deposited a thermally evaporated 100 nm SnO2 film on a pentacene TFT prior to IBAD as a buffer layer. After encapsulation, our TFT showed initial degradation in terms of field-effect mobility (from 0.62 to 0.5 cm(2)/V s). However, the mobility of 0.5 cm(2)/V s was sustained up to 1 month in air and before degrading to 0.35 cm(2)/V, which is but three times higher than that of a reference TFT without no encapsulation treatment. Under the SnO2 encapsulation, on/off current ratio was also maintained at over 10(5) which was initially similar to 10(6), while the unprotected device displayed less than similar to 10(4). Our work demonstrates that the IBAD SnO2 encapsulation is a promising technique for long-term protection of a pentacene TFT. (c) 2005 The Electrochemical Society.