A nano-structure semiconductor light emitting device includes a base layer formed of a first conductivity type semiconductor, and a first insulating layer disposed on the base layer and having a plurality of first openings exposing partial regions of the base layer. A plurality of nanocores is disposed in the exposed regions of the base layer and formed of the first conductivity-type semiconductor. An active layer is disposed on surfaces of the plurality of nanocores and positioned above the first insulating layer. A second insulating layer is disposed on the first insulating layer and has a plurality of second openings surrounding the plurality of nanocores and the active layer disposed on the surfaces of the plurality of nanocores. A second conductivity-type semiconductor layer is disposed on the surface of the active layer positioned to be above the second insulating layer.