The incorporation of Au atoms within the silicon lattice was determined from X-ray absorption fine structure (XAFS). A detection limit of about 1014cm-2 doses equivalent Au atoms in silicon was achieved by grazing incidence of the X-rays and fluorescence detection. Our results are (i) after Au implantation (as-implanted state) single Au atoms occupy regular high symmetric substitutional lattice sites in silicon, (ii) after thermal treatments some of the Au-atoms remain substitutional other diffuse to the sample surface. For the Au atoms near the surface very similar short range parameters as for metallic gold are detected and X-ray reflectrometry gives evidence for a near-surface segregation of gold atoms.