Communication: Rectifying junctions prepared from silicon nanocrystals (Si-nc) by a wet colloid chemical approach are reported. The ultrathin junctions consisted of a derivatized p- or n-type silicon wafer, to which colloidal Si-nc-prepared by sonication of porous silicon in toluene-was attached covalently by self-assembly, and a polypyrrole layer (see Figure). The rectification behavior of various junctions is described.