The chlorine chemisorption geometry fcr both Si(lll) and Ge(lll) surface is considered. Previous theoretical calculations could not give the difference between Cl chemisorbtion on Si (111) and Ge(lll), which was shown by the effects observed in the photoemission with polarized radiation. In this paper the chemisorbed site is determined by the minimization of the total energy calculated by the charge density selfconsistent extended Huckel method. The present calculation shows that Cl adsorbs on the top site of Si (111) surface with covalent binding, which agrees quite well with experiments. While for the case of Ge, calculation shows that both the top site and three-fold site of Cl ehemisorption on the Ge(lll) surface are possible. Since the photoemission by p-polarized and s-polarized radiation did not differ too much for Cl on the Ge(lll) surface, it can not rule out the possibility of top adsorbed site for