A thin film transistor array panel includes: a gate line including a gate electrode; a first gate insulating layer on the gate line; a semiconductor layer on the first gate insulating layer and overlapping the gate electrode; a second gate insulating layer on the semiconductor layer and the first gate insulating layer, and an opening in the second gate insulating layer and through which the semiconductor layer is exposed; drain and source electrodes on the second gate insulating and semiconductor layers and facing each other; a first field generating electrode; and a second field generating electrode connected to the drain electrode. The semiconductor layer includes an oxide semiconductor layer, and first and second auxiliary layers on the oxide semiconductor layer and separated from each other. An edge of the drain and source electrodes is disposed inside an edge of the first and second auxiliary layers, respectively.