Wet-chemical etching of non-polar GaN films can be applied to form textured surfaces that enhance light extraction efficiency in light-emitting diodes. The etch-induced shapes (trigonal prisms) on the sidewalls of concave and convex mesa patterns defined on a-plane GaN films exhibited an alignment towards the [0001] direction. An etch-rate vector model that includes one fast etching direction and two etching directions normal to the fast direction was developed to explain the creation of the etch-induced trigonal prisms. The large lattice parameter along with [000 (1) over bar] and single dangling bond of a-plane surface supply enough space for attack of OH- ions, which is confirmed by XPS analysis that indicates the increased hydroxide spectra on a-plane after KOH etching and these are the reason for different etch rate and formation of trigonal prisms. (C) 2016 Elsevier B.V. All rights reserved.