Phone: þ82 31 290 7134, Fax: þ82 31 290 7941We report the roles of post-deposition annealing of PVP/ pentacene double-layered films on the electrical properties of organic thin film transistors (OTFTs). Data obtained by atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques demonstrate that both the grain size and the (001) peak intensity of pentacene films increase as the annealing temperature increases, resulting in clear dendrite structure after annealing at 100 8C in N 2 ambient. These physical properties were also confirmed by electrical conductivity (EC) of pentacene films. The electrical properties of OTFTs were improved with increasing the annealing temperature in general: Especially, mobility and on/off ratio of the OTFTs subjected to the 100 8C annealing process were 0.32 cm 2 /Vs and 10 6 , respectively, which were both improved at least one order of magnitude as compared to those measured from the samples without annealing.