Recent progress in the understanding of the growth kinetics of Si and SiGe GSMBE using silane and silane/germane mixtures have been reviewed. By detailed analyses of growth rate and surface hydrogen coverage as a function of growth temperature and silane/germane mixing ratio, kinetics of silane/germane adsorption process and hydrogen desorption process has been clarified. A silane molecule requires four adsorption sites on its adsorption onto Si(100) surface, which is mostly due to the simultaneous adsorption of the four hydrogen atoms of the molecule. Hydrogen desorption kinetics on Si(100) surface varies considerably depending on the surface: clean surface, grown surface, or growing surface. Conventional understandings on the effects of mixing germane in Si GSMBE are also challenged. The observed enhancement of the hydrogen desorption with Ge incorporation is caused mostly by increase of the preexponential factor rather than the previously reported decrease of the activation energy.