A display device (10; 20; 30; 40; 50), comprising: a substrate; and a light-emitting unit disposed on the substrate; wherein the light-emitting unit comprises: a first conductive layer overlapping a second conductive layer; a first semiconductor layer disposed between the first conductive layer and the second conductive layer; a second semiconductor layer disposed between the first semiconductor layer and the first conductive layer, the second semiconductor layer comprising a first surface adjacent to the first conductive layer and a second surface opposite to the first surface; a quantum well structure disposed between the first semiconductor layer and the second semiconductor layer, the quantum well structure being adjacent to the second surface of the second semiconductor layer; a via hole penetrated through the first semiconductor layer and the quantum well structure; and a conductive material disposed in the via hole, wherein the second conductive layer is electrically connected with the second semiconductor layer through the conductive material; characterized in that the conductive material disposed in the via hole contacts the second surface of the second semiconductor layer. a substrate; and a light-emitting unit disposed on the substrate; wherein the light-emitting unit comprises: a first conductive layer overlapping a second conductive layer; a first semiconductor layer disposed between the first conductive layer and the second conductive layer; a second semiconductor layer disposed between the first semiconductor layer and the first conductive layer, the second semiconductor layer comprising a first surface adjacent to the first conductive layer and a second surface opposite to the first surface; a quantum well structure disposed between the first semiconductor layer and the second semiconductor layer, the quantum well structure being adjacent to the second surface of the second semiconductor layer; a via hole penetrated through the first semiconductor layer and the quantum well structure; and a conductive material disposed in the via hole, wherein the second conductive layer is electrically connected with the second semiconductor layer through the conductive material; a first conductive layer overlapping a second conductive layer; a first semiconductor layer disposed between the first conductive layer and the second conductive layer; a second semiconductor layer disposed between the first semiconductor layer and the first conductive layer, the second semiconductor layer comprising a first surface adjacent to the first conductive layer and a second surface opposite to the first surface; a quantum well structure disposed between the first semiconductor layer and the second semiconductor layer, the quantum well structure being adjacent to the second surface of the second semiconductor layer; a via hole penetrated through the first semiconductor layer and the quantum well structure; and a conductive material disposed in the via hole, wherein the second conductive layer is electrically connected with the second semiconductor layer through the conductive material; characterized in that the conductive material disposed in the via hole contacts the second surface of the second semiconductor layer.