A semiconductor device comprising: a conductive substrate; a light emitting structure comprising a first conductivity type semiconductor layer, a second conductivity type semiconductor layer, an active layer disposed between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer, and a plurality of recesses, wherein each recess passes through the second conductivity type semiconductor layer and the active layer and extends into a portion of the first conductivity type semiconductor layer; a plurality of first electrodes, each of which is disposed in each of the plurality of recesses, and electrically connected to the first conductivity type semiconductor layer; a second electrode electrically connected to the second conductivity type semiconductor layer, and an insulation layer disposed in each of the plurality of recesses and extended to a first surface of the second conductivity type semiconductor layer where the second conductivity type semiconductor layer is in contact with the second electrode wherein the first conductivity type semiconductor layer, the second conductivity type semiconductor layer, and the active layer include Aluminum respectively, wherein a total area of the plurality of recesses ranges from 13% to 30% of the maximum horizontal sectional area of the light emitting structure and an area of where the second electrode is in contact with the second conductive semiconductor layer ranges from 35% to 70% of the maximum horizontal sectional area of the light emitting structure, characterized in that light emitted from the active layer has a main peak in the range of 100 nm to 320 nm, wherein the insulation layer and the second electrode are spaced apart from each other on the lower surface of the second conductivity type semiconductor layer. a conductive substrate; a light emitting structure comprising a first conductivity type semiconductor layer, a second conductivity type semiconductor layer, an active layer disposed between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer, and a plurality of recesses, wherein each recess passes through the second conductivity type semiconductor layer and the active layer and extends into a portion of the first conductivity type semiconductor layer; a plurality of first electrodes, each of which is disposed in each of the plurality of recesses, and electrically connected to the first conductivity type semiconductor layer; a second electrode electrically connected to the second conductivity type semiconductor layer, and an insulation layer disposed in each of the plurality of recesses and extended to a first surface of the second conductivity type semiconductor layer where the second conductivity type semiconductor layer is in contact with the second electrode wherein the first conductivity type semiconductor layer, the second conductivity type semiconductor layer, and the active layer include Aluminum respectively, wherein a total area of the plurality of recesses ranges from 13% to 30% of the maximum horizontal sectional area of the light emitting structure and an area of where the second electrode is in contact with the second conductive semiconductor layer ranges from 35% to 70% of the maximum horizontal sectional area of the light emitting structure, characterized in that light emitted from the active layer has a main peak in the range of 100 nm to 320 nm, wherein the insulation layer and the second electrode are spaced apart from each other on the lower surface of the second conductivity type semiconductor layer.