Disclosed is an organic thin film transistor, including a substrate, a gate electrode, a gate insulating layer, an organic semiconductor layer, and source/drain electrodes, in which a fluorine-based polymer thin film is provided between the source/drain electrodes and the organic semiconductor layer. A method of fabricating such an organic thin film transistor is also provided. According to example embodiments, the organic thin film transistor may have increased charge mobility and an Ion/Ioff ratio, due to decreased contact resistance between the source/drain electrodes and the organic semiconductor layer. Moreover, upon the formation of the organic semiconductor layer and insulating film, a wet process may be more easily applied, thus simplifying the fabrication process and decreasing the fabrication cost.