A semiconductor light emitting device and a fabrication method thereof are provided. The semiconductor light emitting device includes a light emitting structure including a first conductivity-type semiconductor layer, an active layer, and a second conductivity-type semiconductor layer. A reflective structure is formed on the light emitting structure and includes a nano-rod layer comprised of a plurality of nano-rods and air filling space between the plurality of nano-rods and a reflective metal layer formed on the nano-rod layer.