Disclosed is a light emitting device having vertically stacked light emitting diodes. It comprises a lower semiconductor layer of a first conductive type positioned on a substrate, a semiconductor layer of a second conductive type on the lower semiconductor layer of a first conductive type, and an upper semiconductor layer of a first conductive type on the semiconductor layer of a second conductive type. Furthermore, a lower active layer is interposed between the lower semiconductor layer of a first conductive type and the semiconductor layer of a second conductive type, and an upper active layer is interposed between the semiconductor layer of a second conductive type and the upper semiconductor layer of a first conductive type. Accordingly, there is provided a light emitting device having a structure in which a lower light emitting diode comprising the lower active layer and an upper light emitting diode comprising the upper active layer are vertically stacked. Therefore, light output per unit area of the light emitting device is enhanced as compared with a conventional light emitting device, and thus, a chip area of the light emitting device needed to obtain the same light output as the conventional light emitting device can be reduced.