We report that nanostructured patterns can be achieved on GaN/Al2O3 by a nanofabrication method that employs the inductively coupled plasma (ICP) etching of block copolymer templates. We first prepared the nanoporous patterns of a poly(ethylene oxide-b-methyl methacrylate-b-styrene) (PEO-b-PMMA-b-PS) triblock copolymer thin film on GaN/c-Al2O3 substrates. Then, the nanostructures from PEO-b-PMMA-b-PS triblock copolymers were successfully transferred to GaN layers using ICP etching. Room temperature photoluminescence (PL) confirmed that the PL intensity was increased by about 30% around 450 nm wavelength after the pattern transfer onto GaN/c-Al2O3 substrates.