We present a spray based-method for the formation and production of semiconductor nanocrystals that provides an attractive alternative to the commonly used epitaxial and colloidal procedures. According to this spray-based method, mainly thermospray, solutions of semiconductor salts are first sprayed into monodispersed droplets, which subsequently become solid nanocrystals by solvent evaporation. A semiconductor nanocrystal is produced from a single spray droplet upon the full vaporization of the solvent. The average diameter and size distribution of the final nanocrystals are controlled and determined by the solute concentration of the sprayed solution and by the droplet size, hence by the spray production parameters. The spray-produced nanocrystals are collected on any selected solid support. Representative results, shown in this letter, reveal the formation of CdS nanocrystals in the size range of 3 to 6 nanometers and with a size distribution of as low as five percent. A further structural analysis of these nanocrystals showed that they were formed in the zinc blende phase with a high degree of crystallinity.