Silk fibroin, one of the silk proteins produced by the silk work, is shown to be an excellent gate dielectric material for pentacene organic thin-film transistors (OTFTs). The pentacene OTFT described exhibits a very high field-effect mobility value of 23.2 cm(2) V (1) s (1) and a low operating voltage of -3 V. This, combined with its advantages of low cost and light weight, confers on it great potential for high-speed flexible electronics applications.