A nanostructure semiconductor light emitting device may include a first conductivity-type semiconductor base layer, a mask layer disposed on the base layer and having a plurality of openings exposing portions of the base layer, a plurality of light emitting nanostructures disposed in the plurality of openings, and a polycrystalline current suppressing layer disposed on the mask layer. At least a portion of the polycrystalline current suppressing layer is disposed below the second conductivity-type semiconductor layer. Each light emitting nanostructure includes a first conductivity-type semiconductor nanocore, an active layer, and a second conductivity-type semiconductor layer.