A method of manufacturing a thin film transistor is capable of enhancing pattern precision of an organic semiconductor layer and simplifying a patterning process. The method includes forming an organic insulating film on a substrate and forming a bank having the first and second concave portions and a third concave portion in the organic insulating film, the third concave portion being formed on the first and second concave portions. The method further includes forming a source electrode and a drain electrode in the first and second concave portions and forming an active layer in the third concave portion, the active layer contacting the source electrode and the drain electrode.