GaN(0001)/c-Al2O3 is etched by simultaneous irradiation with an F-2 laser and a KrF excimer laser. The use of an F-2 laser in addition to a KrF excimer laser reduces the roughness of the GaN surface compared with the case of KrF irradiation etching. An F-2 laser, below the etching threshold, simultaneously irradiated with a KrF excimer laser, decreases the etching rate due to an increase in the absorption coefficient of the sample surface against the KrF excimer laser. A very sharp etching sidewall and flat surface are obtained when the etching depth reaches the Al(2)o(3) substrate.