Photo-assisted wet chemical etching of GaN thin film was studied using KOH based solutions. A 2μm-2μm titanium line-and-space pattern was used as a etching mask. It is found that the etching characteristics of the GaN thin film is strongly dependent on the pattern direction by unisotropic property of KOH based solution. When the pattern was aligned to the [1120] directions, (101n)-facet is revealed constructing V-shaped sidewalls.