High index surfaces of group-IV crystals are important because high index facets often appear during heteroepitaxial growth of Ge and SiGe islands on Si(001) and Si(111), The Si(113) surface is of a particular interest : Suitable for epitaxy, atomically hat, and thermally stable Si(113) can be easily obtained, Results are reported of scanning tunneling microscopy investigation of the effect of antimony adsorption on Si(113)3x2 at low coverages as a function of annealing temperature, At room temperature. Sb, molecules are physisorbed in a metastable precursor state and move mainly into areas of high density of antiphase boundaries and other defects where they are chemisorbed. Several cluster formations of different size, shape, and orientation are observed. During annealing at first some of the clusters dissociate and some arrange along [1(1) over bar0$] and [3(2) over bar3$], With increasing temperature (about 550 degrees C), the clusters break and Sb atoms are incorporated into the surface. On the basis of nb initio calculation, an atomic structural model for the resulting 2x2 reconstruction is proposed and verified.