A pentacene (C22H14)-based high-voltage organic thin-film transistor (HVOTFT) was demonstrated on both a rigid and a flexible substrate. The HVOTFT showed minimal degradation of the current-voltage (I-V) characteristics under flexure. Consistent with the previous reports on amorphous silicon (a-Si) TFTs, the offset drain/source structure enabled high-voltage operation, allowing for the HVOTFT to switch very large drain-to-source voltages (VDS > 300 V) with a relatively lower controlling voltage (0 V