An electron accumulation-mode operation in organic field-effect transistor (OFET) using a thin film of copper phthalocyanine (CuPc) and Ca source-drain electrodes was demonstrated. Appearance of the electron accumulation -mode in OFET was ascribed to the lowering of barrier for electron injection at a source electrode. The OFET also showed a p-channel and typical ambipolar transport property. The field-effect electron mobility of 1.0 x 10(-3) cm(2)/V s and field-effect hole mobility of 2.5 x 10(-4) cm(2) /Vs s were estimated from the saturation currents above the threshold voltage. (C) 2004 Elsevier B.V. All rights reserved.