We report the evolution of sharp conical spike array formed on the silicon surface under the cumulative picosecond (ps) and femtosecond (fs) laser pulse irradiations in SF6 ambient. The experimental results suggest that the physical mechanisms of conical spike evolutions under ps and fs laser irradiations are different. Under the ps laser irradiation, silicon surface is melted before the spike arrays formed, while under the fs laser irradiation, the formation of spike arrays does not pass through the liquid phase. The evolution of microstructure is strongly dependent on the laser duration. © 2004 Elsevier B.V. All rights reserved.