We report the strategy of controlling the surface properties of polymethylsilsesquioxane (PMSQ) films by a silane-coupling agent. The surface properties of chemically modified PMSQ films are investigated by the water contact angle and Fourier transform infrared (FTIR) measurements. The FTIR spectra show the distinct change of the silanol peaks before and after octadecyltrichlorosilane (OTS) treatments of PMSQ films. The OTS-modified PMSQ films exhibit a high water contact angle of 100 degrees. which is much higher than that of non-treated PMSQ films (89 degrees). The electrical performances of organic thin-film transistors are enhanced by the surface modification of PMSQ films using OTS as the silane-coupling agent. (C) 2008 Elsevier B.V. All rights reserved.