The process of laser ablation of silicon targets with approximate to 1 ps/1055 nm and 100 fs/780 nm laser pulses has been investigated by exploiting optical emission spectroscopy and fast photography of the ablated species in the gas phase, and atomic force microscopy of less than one layer deposits of the ablated material. We have observed, for both durations, the presence of a fast atomic component followed by a much slower plume of nanoparticles of the target material. For both laser pulses, experimental ablation thresholds have been compared with the prediction of a simple theoretical model, resulting in pretty good agreement. The properties of size distribution of the silicon nanoparticles have been analyzed as a function of the laser pulse intensity, and also compared with the results for metallic targets. Our experimental results show that the generation of nanoparticles, with pretty narrow size distributions, is a characteristic feature of the interaction of ultrashort laser pulses with solids (namely, metals and semiconductors), for both approximate to 1 ps and approximate to 100 fs laser pulse durations. (c) 2005 Elsevier B.V. All rights reserved.