We investigated the effects of treatment with octadcyltrichlorosilane (OTS) and the charge transfer molecules (CTM) such as 2-mercapto 5-nitrobenzimidazole (NWB), 2-mercapto benzoxazole (MBX), 2-mercapto benzthiazole (MBT), and 2-mercapto 5-methylbenzimidazole (MMB) on SiO2 and Au electrode on pentacene organic thin film transistors (OTFTs). Especially for improvement of the mobility and the contact resistance at the same time, we simultaneously treated SiO2 and Au electrode with OTS, NTNB, and MBX. As the results, we could improve the mobility to 0.2 CM2/V s and reduce the contact resistance to 50 k Omega, corresponding to 10 times larger than the untreated OTFTs. (c) 2004 Elsevier B.V. All rights reserved.