We have investigated the electrical properties of top-contact type copper phthalocyanine (CuPc) based field effect transistors prepared on various high dielectric constant (high-K) gate oxide thin films, such as tantalum oxide (epsilon(r) similar to 20), tantalum oxide/silicon dioxide (epsilon(r) similar to 6), and aluminum oxide (epsilon(r) similar to 8) prepared by RF magnetron sputtering. A low operating voltage of less than 6 V and a field effect mobility P c p, of 3.8 x 10(-3) cm(2)/V s, which is higher than It c p obtained with Al2O3 ant TA(2)O(5) + SiO2, was obtained in the CuPc FET prepared on 200-nm-thick TA(2)O(5). The FET properties were then combined with the electrical properties of metal-insulator-semiconductor (MIS) capacitors. The doping profile in CuPc was calculated from the capacitance-voltage (C-V) measurement using the FET with patterned CuPc, and it was found that there is a very high density of electronic states exist especially near the interface, which were considered as a origin of the large interfacial capacitance. It was also found that the subthreshold slope depends on the gate capacitance and the considerable interfacial capacitance with a thickness of only 3-4 nm in the CuPc based FETs prepared on various oxide films. (c) 2005 Elsevier B.V. All rights reserved.