We present a new method for the deposition of colloidal Au nanoparticles on the surface of silicon substrates based on short-time Ar plasma treatment without the use of any polymeric layers. The elaborated method is compatible with molecular beam epitaxy, which allowed us to carry out the detailed study of GaAs nanowire synthesis on Si(111) substrates using colloidal Au nanoparticles as seeds for their growth. The results obtained elucidated the causes of the difference between the initial nanoparticle sizes and the diameters of the grown nanowires.