Effects of atomic hydrogen annealing (AHA) on the film properties and the electrical characteristics of pentacene organic thin-film transistors (OTFTs) are investigated. The surface energy of SiO₂ surface and grain size of pentacene film were decreased with increasing AHA treatment time. For the treatment time of 300s, pentacene film showed the (00l) and (011') orientation and high carrier mobility in spite of small crystal grain.