Improvement of the on/off ratio in carrier-generation type organic field-effect transistors with pentacene and MoO3 layers was attempted using oblique deposition. A MoO3 layer was formed only between the gold (Au) source and the drain electrodes, and devices with a MoO3 layer evaporated under various deposition angles were fabricated. A formation of a MoO3-free area is expected adjacent to the source or drain electrode by the oblique deposition. The off-current in the device decreased and the on/off ratio was increased with increasing deposition angle, and we achieved a fabricating device with a MoO3 layer having high on/off ratio, almost the same as that of the device without the MoO3 layer. From those results, we deduced that charge-transfer (CT) complexes at the pentacene/MoO3 interface formed a high-conductive path for the off-current, and the off-current was reduced by the formation of a highly-resistive MoO3-free area between electrodes. Therefore, controlling the CT complex layer formation by patterning the MoO3 layer can reduce the amount of off-current and improve the on/off ratio. (C) 2016 The Japan Society of Applied Physics