An organic light-emitting display device comprises a first thin-film transistor disposed on a substrate; and a second thin-film transistor disposed on the substrate and spaced apart from the first thin-film transistor. The first thin-film transistor comprises a first semiconductor layer, a first conductive layer disposed on the first semiconductor layer and that overlaps the first semiconductor layer, and a first insulating layer disposed between the first semiconductor layer and the first conductive layer. The second thin-film transistor comprises a second semiconductor layer, and a second conductive layer disposed on the second semiconductor layer and that overlaps the second semiconductor layer. The first semiconductor layer is disposed on a layer higher than the second semiconductor layer, the first semiconductor layer comprises an oxide semiconductor, the second semiconductor layer comprises low temperature polycrystalline silicon (LTPS), and the first insulating layer covers the entire first semiconductor layer.