A wet-chemical process has been developed to passivate the Si(100) surface with sulfur (S) in an aqueous solution. The solution contains an etchant for SiO 2 , ammonium hydroxide [NH 4 OH] and a passivant for the surface, ammonium sulfide [(NH 4 ) 2 S]. The compatibility of the etchant with the passivant allows SiO 2 , native or thermal, to be removed in situ from the surface. A fresh and clean Si(100) surface is exposed right before it is passivated by S. Schottky barrier heights of Al on S-passivated n- and p-type Si(100) show a greater sensitivity to Al work function and Si electron affinity, suggesting good-quality passivation.