A nitride-based semiconductor light emitting device having an improved structure in which light extraction efficiency is improved and a method of manufacturing the same are provided. The nitride-based semiconductor light emitting device comprises an n-clad layer, an active layer, and a p-clad layer, which are sequentially stacked on a substrate, wherein the n-clad layer comprises a first clad layer, a second clad layer, and a light extraction layer interposed between the first clad layer and the second clad layer and composed of an array of a plurality of nano-posts, the light extraction layer diffracting or/and scattering light generated in the active layer.