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 . <EOS>