Provided are an organic TFT that reduces contact resistance between a source and drain electrode and an organic semiconductor layer and that can be easily manufactured, a flat panel display device having the organic TFT, and methods of manufacturing the organic TFT and the flat panel display device having the same. The organic TFT includes; a substrate; a gate electrode and a blocking layer formed on the substrate; a gate insulating film covering the gate electrode and the blocking layer; a source electrode and a drain electrode located on the gate insulating film; an auxiliary source electrode and an auxiliary drain electrode respectively located on the source electrode and the drain electrode; and an organic semiconductor layer contacting the auxiliary source electrode and the auxiliary drain electrode.