The ablative decomposition of GaN films induced with a XeC1 excimer laser (? = 308 nm) was investigated for a potentially low-damage surface planarization process. Samples, 2-tm-thick, were grown on (0001) sapphire by ammonia molecular beam epitaxy. They had a characteristic micro-hillock type surface morphology with a roughness, averaged over 5 x 5 tm2 area, typically, of 13 nm. Following the laser irradiation, this roughness could be reduced to 3.6 urn. The results indicate that the ablation process follows the Lambert-Beer's law, with an absorption coefficient of 3 x iO cm'. The experiment was carried out with relatively short pulses ('r =10 ns), which appear to be responsible for the observed onset of the laser-induced decomposition of GaN and surface planarization at significantly smaller laser fluences than reported in the literature. The ability to carry out decomposition of GaN with low laser fluences is of practical importance for achieving a low-damage GaN planarization process and/or intentional delaminating of this material from the sapphire substrate by the back side irradiation technique.