A semiconductor light emitting device includes a light emitting structure having a first conductivity-type semiconductor layer, an active layer, and a second conductivity-type semiconductor layer, a transparent electrode layer on the second conductivity-type semiconductor layer, and a reflective electrode structure on the transparent electrode layer that includes a light-transmitting insulating layer on the transparent electrode layer with insulating patterns, portions of sides of the insulating patterns being open, and a contact region of the transparent electrode layer being defined by a region between the insulating patterns, air gaps between the transparent electrode layer and the insulating patterns, the air gaps extending in the open portions of the sides of the insulating patterns, and a reflective electrode layer on the insulating patterns to cover the open portions of the insulating patterns, the reflective electrode layer being connected to the contact region of the transparent electrode layer.