The organic TFT includes: a gate electrode; source and drain electrodes insulated from the gate electrode; an organic semiconductor layer insulated from the gate electrode and electrically connected to the source and drain electrodes; an insulating layer insulating the gate electrode from the source and drain electrodes and the organic semiconductor layer; and a self-assembly monolayer (SAM) included between the insulating layer and the organic semiconductor layer. A compound forming the SAM has at least one terminal group selected from the group consisting of an unsubstituted or substituted C6-C30 aryl group and an unsubstituted or substituted C2-C30 heteroaryl group. The organic TFT is formed by forming the above-described layers and forming the SAM on the insulating layer before the organic semiconductor layer and source and drain electrodes are formed. Thus, the adhesive force between the organic semiconductor layer and the insulating layer increases and the phase separation of the organic semiconductor material caused by heat can be prevented, thereby obtaining a flat panel display device with improved reliability.