The system Si/GaAs(110) was studied by surface extended x-ray absorption fine structure at the silicon K edge, starting from a 0.5 monolayer (ML) coverage up to 3 ML. At very low coverages, the first adsorption site of the silicon has been determined to be above the center of the triangle formed by two arsenic and one gallium surface atoms. The growth mode of silicon on this surface obeys a modified version of the Stranski-Krastanov model : the formation of three-dimensional clusters appears at 2.5 ML and involves all the deposited silicon atoms.