Abstract: A method of manufacturing a semipolar semiconductor crystal comprising a group-III-nitride (III-N), the method comprising: providing a substrate comprising sapphire (Al2O3) having a first surface that intersects c-planes of the sapphire; forming a plurality of trenches in the first surface, each trench having a wall whose surface is substantially parallel to a c-plane of the substrate; epitaxially growing a group-III-nitride (III-N) material in the trenches on the c-plane surfaces of their walls until the material overgrows the trenches to form a second planar surface, substantially parallel to a (20-2l) crystallographic plane of the group-III-nitride, wherein l is an integer.