Picene, a p-type organic semiconductor, was involved as active layer in organic thin film transistors (OTFTs). Picene thin films were realized by vacuum evaporation on gate dielectrics based on bare silicon dioxide (SiO2) or coated with polymethyl-methacrylate (PMMA). Assisted by a controlled post-deposition annealing at low temperature (<100 degrees C), OTFTs were characterized in air to provide a hole mobility up to 0.2 cm(2)/V s. Thin-film morphology and microstructure were studied in details by atomic force microscopy (AFM) and X-ray film diffractometry (XRD) before and after the post-annealing as thickness and vacuum conditions dependences. While any molecular reorganization was induced by such thermal post-treatment, the unavoidable presence of H2O molecules in air and their diffusion in thin films were consistently reduced to offer air-operating OTFTs. (C) 2014 Elsevier B.V. All rights reserved.