A semiconductor light emitting device is provided that may include: a light emitting structure in which a conductive substrate, a second conductive type semiconductor layer, an active layer, and a first conductive type semiconductor layer are stacked; a diffusion metal layer and an insulating layer disposed between the conductive substrate and the second conductive type semiconductor layer; and areflecting electrode layer disposed under the second conductive type semiconductor layer, wherein a top surface of the reflecting electrode layer, facing the second conductive type semiconductor layer, has a smaller area than a bottom surface of the second conductive type semiconductor layer, the diffusion metal layer forms a plurality of via holes extended to an inside of the first conductive type semiconductor layer through the insulating layer, the second conductive type semiconductor layer, and an active layer, and electrically couples the diffusion metal layer to the first conductive typesemiconductor layer through the via holes, and a shortest distance D2 between an arbitrary via hole and another via hole adjacent to the via hole is larger than a shortest distance D3 between the viahole which is the closest to an outside of the first conductive type semiconductor layer and an outside of the second conductive type semiconductor layer.