For Si epitaxial growth on Si(lll) with dichlorosilane (SiH2Cl2), the kinetics of nucleation and growth of pyramidal hillock (PH)has been investigated by measuring the variations of size and density of PH as a function of growth temperature, SiH2Cl2 volume concentration, and gas pressure. The nucleation of PH can be considerably suppressed by reducing SiH2Cl2 volume concentration or gas pressure under a constant SiH2Cl2 mole concentration. The reason for the reduction in PH density is discussed in terms of the previous findings that the nucleation of PH is always associated with the existence of growth defects such as stacking faults, dislocations, or polycrystalline Si. Furthermore, the PH size increases in proportion to the layer thickness and decreases drastically as the PH density increases or the growth temperature is raised. This indicates that the growth of PH is dominated by three factors : layer thickness, distribution of Si adatoms into the individual PH, and surface migration of Si adatoms. Thus it is likely that PH plays a role of growth site as kink and step edge, whereas Si adatoms are more preferentially incorporated into step and kink sites during Si growth.