The bottom contact pentacene-based thin-film transistor is fabricated, and it is treated by rapid thermal annealing (RTA) with the annealed temperature up to 240 degrees C for 2 min in the vacuum of 1.3 x 10(-2) tort. The morphology and structure for the pentacene films of OTFTs were examined by scanning electron microscopy and X-ray diffraction technique. The thin-film phase and a very small fraction of single-crystal phase were found in the as-deposited pentacene films. While the annealing temperature increases to 60 degrees C. the pentacene molecular ordering was significantly improved though the grain size only slightly increased. The device annealed at temperature of 120 degrees C has optimal electrical properties, being consistent with the experimental results of XRD. The post-annealing treatment results in the enhancement of field-effect mobility in pentacene-based thin-film transistors. The field-effect mobility increases from 0.243 cm(2)/V s to 0.62 cm(2)/V s. Besides, the threshold voltage of device shifts from -7 V to -3.88 V and the on/off current ratio increases from 4.0 x 10(3) to 8.7 x 10(3). (C) 2011 Elsevier Ltd. All rights reserved.