A method of manufacturing a thin film transistor (“TFT”) substrate includes forming a gate insulating film and an active layer on a substrate, forming a data metal layer including a first, second, and third metal layers on the active layer, forming a first photoresist pattern on the data metal layer, dry-etching the third metal layer by using the first photoresist pattern, simultaneously dry-etching the second and first metal layers by using the first photoresist pattern, dry-etching the active layer by using the first photoresist pattern, etching the first photoresist pattern to form a second photoresist pattern by which the channel region is removed and forming a source electrode and a drain electrode by dry-etching the channel region of the data metal layer by using the second photoresist pattern.