A light emitting device includes a substrate having a patterned surface and formed with a plurality of spaced apart cavities, and an epitaxial layer formed on the patterned surface of the substrate, having a patterned surface that is in face-to-face contact with the patterned surface of the substrate, and formed with a plurality of protrusions that protrude from the patterned surface of the epitaxial layer and that are respectively received in the cavities. Each of the protrusions is polygonal in shape and defines a plurality of vertices. The vertices of each of the protrusions contact the cavity-defining wall of the respective one of the cavities so as to form a plurality of closed pores between each of the protrusions and the cavity-defining wall of the respective one of the cavities.