A light source device having a monolithic structure and comprising: a substrate; a light source array, comprising a plurality of first semiconductor light emitting elements and a plurality of second semiconductor light emitting elements disposed on the substrate and spaced apart from each other; wherein each of the first semiconductor light emitting elements comprises: a first reflective layer; a first light emitting layer configured to emit light of a first wavelength; a first etch stop layer; a second light emitting layer configured to emit light of a second wavelength, the second wavelength being different from the first wavelength; and a first nanostructure reflective layer; and wherein each of the second semiconductor light emitting elements comprises: a second reflective layer having same material and thickness as the first reflective layer; a third light emitting layer having same material and structure as the second light emitting layer, the third light emitting layer being configured to generate light of the second wavelength; a second etch stop layer having same material and thickness as the first etch stop layer; and a second nanostructure reflective layer; wherein the first light emitting layer and the second light emitting layer are disposed between the first reflective layer and the first nanostructure reflective layer, the first reflective layer and the first nanostructure reflective layer forming a resonance cavity with respect to light generated in the first light emitting layer, wherein the third light emitting layer is disposed between the second reflective layer and the second nanostructure reflective layer, wherein the first etch stop layer is disposed between the first light emitting layer and the second light emitting layer, and wherein the second etch stop layer is disposed between the third light emitting layer and the second nanostructure reflective layer; and wherein the light source array is configured to selectively drive the plurality of first semiconductor light emitting elements or the plurality of second semiconductor light emitting elements, such that light of different wavelengths may be selectively emitted. a substrate; a light source array, comprising a plurality of first semiconductor light emitting elements and a plurality of second semiconductor light emitting elements disposed on the substrate and spaced apart from each other; wherein each of the first semiconductor light emitting elements comprises: a first reflective layer; a first light emitting layer configured to emit light of a first wavelength; a first etch stop layer; a second light emitting layer configured to emit light of a second wavelength, the second wavelength being different from the first wavelength; and a first nanostructure reflective layer; and a first reflective layer; a first light emitting layer configured to emit light of a first wavelength; a first etch stop layer; a second light emitting layer configured to emit light of a second wavelength, the second wavelength being different from the first wavelength; and a first nanostructure reflective layer; and wherein each of the second semiconductor light emitting elements comprises: a second reflective layer having same material and thickness as the first reflective layer; a third light emitting layer having same material and structure as the second light emitting layer, the third light emitting layer being configured to generate light of the second wavelength; a second etch stop layer having same material and thickness as the first etch stop layer; and a second nanostructure reflective layer; a second reflective layer having same material and thickness as the first reflective layer; a third light emitting layer having same material and structure as the second light emitting layer, the third light emitting layer being configured to generate light of the second wavelength; a second etch stop layer having same material and thickness as the first etch stop layer; and a second nanostructure reflective layer; wherein the first light emitting layer and the second light emitting layer are disposed between the first reflective layer and the first nanostructure reflective layer, the first reflective layer and the first nanostructure reflective layer forming a resonance cavity with respect to light generated in the first light emitting layer, wherein the third light emitting layer is disposed between the second reflective layer and the second nanostructure reflective layer, wherein the first etch stop layer is disposed between the first light emitting layer and the second light emitting layer, and wherein the second etch stop layer is disposed between the third light emitting layer and the second nanostructure reflective layer; and wherein the light source array is configured to selectively drive the plurality of first semiconductor light emitting elements or the plurality of second semiconductor light emitting elements, such that light of different wavelengths may be selectively emitted.