Femtosecond pulsed laser-induced periodic surface structure on GaN/sapphire is reported in this paper. It was found that the period of the laser-induced ripples was much dependent on the incident laser fluence. Through finely adjusting laser fluence and pulse number, uniform ripples could be formed on the sapphire surface. We attributed the formation of such periodic two-dimensional structures to optical interference of the incident laser light with scattered waves from a surface disturbance. Also, it was found that the GaN capping layer played a very important role in forming the periodic structures on the sapphire surface. (c) 2005 Elsevier B.V. All rights reserved.