A gallium nitride (GaN) light emitting device and a method of manufacturing the same are provided, the method including sequentially forming a buffer layer and a first nitride layer on a silicon substrate, and forming a plurality of patterns by dry etching the first nitride layer. Each pattern includes a pair of sidewalls facing each other. A reflective layer is deposited on the first nitride layer so that one sidewall of the pair is exposed by the reflective layer. An n-type nitride layer that covers the first nitride layer is formed by horizontally growing an n-type nitride from the exposed sidewall, and a GaN-based light emitting structure layer is formed on the n-type nitride layer.