The electroless deposition of Gold on H-terminated Si(100) substrates has been investigated with 2.0 MeV He + ions Rutherford Backscattering Spectrometry (RBS) and Transmission Electron Microscopy (TEM). A large number of Gold nanoparticles (in excess of 10 11 cm -2 ) was instantaneously generated on the silicon substrate by immersion in a solution containing 1mM KAuCl4 and 4.8M HF. The gold atomic surface concentration, as given by the RBS measurements, increases with the square root of the immersion time from 1 to 5s. The experimental data are fitted with a diffusion coefficient for the metallic ions in the solution of 1.45 × 10 -5 cm 2 s -1 . At longer deposition times, instead, the Au ions flux is constant, with a static boundary layer of few hundred microns thick in agreements with one dimensional diffusion limited mechanism.