In a nitride semiconductor light emitting device having patterns formed on the upper and lower surfaces of a substrate from which light is emitted in a flip chip bonding structure, the patterns are capable of changing light inclination at the upper and lower surfaces of the substrate to decrease total reflection at the interfaces, thereby improving light emitting efficiency. The device includes a substrate having upper and lower surfaces on which predetermined patterns are formed such that light can be incident within a critical angle, the substrate allowing a gallium nitride-based semiconductor material to be grown thereon, an n-type nitride semiconductor layer formed on the upper surface of the substrate, an active layer formed on the upper surface of the n-type nitride semiconductor layer such that the n-type nitride semiconductor layer is partially exposed, a p-type nitride semiconductor layer formed on the upper surface of the active layer, a p-electrode formed on the upper surface of the p-type nitride semiconductor layer, and an n-side electrode formed on the partially exposed n-type nitride semiconductor layer.