Disclosed are GaN based light emitting devices and methods of manufacturing the same using post-mechanical treatment. The GaN based light emitting device includes first and second electrodes, and a flexible substrate which are sequentially stacked, an n-type GaN layer, an activation layer, and a p-type GaN layer interposed between the first and second electrodes and forming a core-shell structure, and a buried layer interposed between the flexible substrate and the first electrode, wherein the first electrode and the core-shell structure are buried in the buried layer.