Organic heterojunction transistors (OHJTs) based on 5,5'"-bis(naphtha-2-yl)-2,2':5",2"-quaterthiophene (NaT4)/copper-hexadecafluoro-phthalocyanine (F16CuPc) heterojunction were fabricated in single-sandwich and sandwich configurations, respectively. All the devices operated in depletion-accumulation (normally-on) mode. High field-effect mobility of 0.35 cm(2)/Vs was obtained for all devices, which was higher than that, 0.20 cm(2)/Vs of the devices with NaT4 as active layer. The on/off ratio of 1 x 10(5) was obtained for OHJTs with single-sandwich configuration, which is three orders of magnitude higher than that of OHJTs with sandwich configuration. Compared with OHJTs with sandwich configuration, the higher on/off ratio was mainly determined by the lower off state current in OHJTs with single-sandwich configuration. In OHJTs with single-sandwich configuration, the well-type shield effect of the source and drain electrodes caused a very narrow empty region in F16CuPc film, which is responsible for the lower off state current. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.