Etching of the GaN layers in 1M KOH aqua solution under irradiation was studied by the electro-stimulated photolysis using N₂-laser (337 nm, 60 W/m²) as a light source. It was observed that the size and the depth of the failure monotonically depend on the optical power and the irradiation time of the N₂ laser and the GaN layer type of conductivity. The GaN layers etching rate was evaluated. A mechanism of the failure in the n-GaN layers is discussed.