A nanostructure semiconductor light-emitting device includes a base layer formed of a first conductivity-type semiconductor, a first material layer disposed on the base layer and including a plurality of openings, a plurality of light-emitting nanostructures, each of which extends through each of the plurality of openings and includes a nanocore formed of a first conductivity-type semiconductor, an active layer and a second conductivity-type semiconductor shell layer, sequentially disposed on the nanocore, a filling layer disposed on the first material layer, wherein the filling layer fills spaces between the plurality of light-emitting nanostructures and a portion of each of the plurality of light-emitting nanostructures is exposed by the filling layer, a second conductivity-type semiconductor extension layer disposed on the filling layer and covering the exposed portion of each of the plurality of light-emitting nanostructures, and a contact electrode layer disposed on the second conductivity-type semiconductor extension layer.