An epitaxial structure having a low defect density includes: a base layer; a first epitaxial layer having a plurality of concentrated defect groups, and an epitaxial surface that has a plurality of first recesses corresponding in position to the concentrated defect groups, the sizes of the first recesses being close to each other; and a plurality of defect-termination blocks respectively and filling the first recesses and having polished surfaces. The defect-termination blocks are made of a material which is different in removal rate from that of the first epitaxial layer. The polished surfaces are substantially flush with the epitaxial surface so that the first epitaxial layer has a substantially planarized crystal growth surface