A pulsed KrF excimer laser of irradiance of about 108 W/cm2 was utilized to synthesize Si nanocrystals on SiO2/Si substrates. The results were compared with that ones obtained by applying low bias voltage to Si(1 0 0) target in order to control the kinetic energy of plasma ions. Glancing incidence X-ray diffraction spectra indicate the presence of silicon crystalline phases, i.e. (1 1 1) and (2 2 0), on SiO2/Si substrates. The average Si nanocrystal size was estimated to be about 45 nm by using the Debye–Scherrer formula. Scanning electron microscopy and atomic force microscopy images showed the presence of nanoparticles of different size and shape. Their distribution exhibits a maximum concentration at 49 nm and a fraction of 14% at 15 nm.