A thin-film transistor substrate may include a first thin-film transistor and a second thin-film transistor which are disposed on a substrate. The first thin-film transistor may include a first semiconductor layer, a first gate electrode, and a first electrode. The second thin-film transistor may include a second semiconductor layer disposed on the first semiconductor layer and overlapping at least a portion of the first semiconductor layer, a second gate electrode, and a second electrode electrically connected to the first electrode. The second electrode may overlap the first electrode.