Bottom-contact (BC) copper phthalocyanine (CuPc) thin film transistor with UV/ozone treated Au as a source/drain electrode was fabricated and the contact resistance was estimated from the transmission line method (TLM). Comparing the properties of OTFT with untreated Au electrode, the performance of the BC CuPc-TFT with the UV/ozone treated Au electrodes was significantly improved: saturation mobility increased from 4.69 x 10(-3) to 2.37 x 10(-2) cm(2)/V s, threshold voltage reduced from -29.1 to -6.4 V, and threshold swing varied from 5.08 to 2.25 V/decade. The contact resistance of the device with UV/ozone treated Au electrodes was nearly 20 times smaller than that of the device with untreated Au electrodes at the gate voltage of -20 V. This result indicated that using the UV/ozone treated Au electrode is an effective method to reduce the contact resistance. The present BC configuration with UV/ozone treated Au electrodes could be a significant step towards the commercialization of OTFT technology. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.