We report on the use of polymer fibers for large-area soft nanolithography on organic and inorganic surfaces with 50 nm resolution. The morphology of fibers and of the corresponding patterned gap is investigated, demonstrating a lateral dimension downscaling of up to nine times, which greatly increases the achieved resolution during pattern transfer. In this way, we realize poly mer field effect transistors with channel length and width as low as 250 nm that are expected to show transistor transition frequency up to a few MHz, and are thus exploitable as low-cost radio-frequency identification devices.