A method of manufacturing a thin film transistor array panel is provided, the method includes forming a gate line on a substrate; forming a gate insulating layer on the gate line; forming a data line and a drain electrode on the gate insulating layer; forming an organic semiconductor layer on the data line, the drain electrode and an exposed portion of the gate insulating layer between the data line and the drain electrodel; forming a protective member fully covering the organic semiconductor layer; forming a passivation layer on the protective layer, the data line, and the drain electrode; forming a contact hole in the passivation layer to expose a portion of the drain electrode; and forming a pixel electrode on the passivation layer, the pixel electrode connected to the drain electrode through the contact hole.