The effects of hydrophobic nanostructures on the growth of pentacene molecules and the electrical characteristics of pentacene thin-film transistors (TFTs) are investigated. X-ray diffraction results show that hydrophobic nanostructures are conducive to the upright growth of pentacene molecules to the substrate. Pentacene TFTs, in which hydrophobic nanostructures with a cowl shape were introduced at the interface between the pentacene layer and the gate insulator, thus exhibit a pronounced enhancement in the field-effect mobility, up to approximately 2.94 cm2/Vs. These results suggest that hydrophobic nanostructures are effective to the ordered growth of pentacene molecules for high-performance organic TFTs.