A semiconductor light emitting device including a first conductive semiconductor base layer on a substrate; an insulating layer on the first conductive semiconductor base layer, the insulating layer including a plurality of openings through which the first conductive semiconductor base layer is exposed; and a plurality of nanoscale light emitting structures on the first conductive semiconductor base layer, the nanoscale light emitting structures respectively including a first conductive semiconductor core on an exposed region of the first conductive semiconductor base layer, and an active layer, and a second conductive semiconductor layer sequentially disposed on a surface of the first conductive semiconductor core, wherein a lower edge of a side portion of each nanoscale light emitting structure is on an inner side wall of the opening in the insulating layer.