A method of fabricating a group III-nitride semiconductor includes the following steps of: forming a first patterned mask layer with a plurality of first openings deposited on an epitaxial substrate; epitaxially growing a group III-nitride semiconductor layer over the epitaxial substrate and covering at least part of the first patterned mask layer; etching the group III-nitride semiconductor layer to form a plurality of second openings, which are substantially at least partially aligned with the first openings; and epitaxially growing the group III-nitride semiconductor layer again.