Collagen hydrolysate is a nature protein, which works well as the gate dielectric for organic thin film transistors (OTFTs). The pentacene OTFTs exhibit a field-effect mobility (µFE) value of 0.8 cm²V-1s-1 and an on/off ratio of 105 in vacuum. The drain current is greatly enhanced and the µFE value increases to ca. 15.5 cm²V-1s-1 when OTFTs are exposed to air. The enhancement of µFE is attributed to the interaction of water and OH-groups in collagen hydrolysate in air ambient. [ABSTRACT FROM AUTHOR]