Disclosed herein are a method for fabricating an organic thin film transistor, including treating the surfaces of a gate insulating layer and source/drain electrodes with a self-assembled monolayer (SAM)-forming compound through a one-pot reaction, and an organic thin film transistor fabricated by the method. According to example embodiments, the surface-treatment of the gate insulating layer and the source/drain electrodes may be performed in a single vessel through a single process.