We studied the dependence of selective epitaxially grown silicon (SEG-Si) shape on the conditions of ultra-high vacuum chemical vapor deposition using disilane (Si2H6) gas, which grew on Si (100) substrates patterned with SiO2 stripes. SEG-Si edges typically formed two types of configurations: facets and bumps. It was confirmed that the shape of SEG-Si edge is strongly dependent on the growth mode of the (100) plane: facet configurations are formed in the mass transfer limited region, and bump configurations are formed in the kinetically limited region. Therefore, it was concluded that the surface migration length of adatoms resulting from the decomposition of Si2H6 molecules is related to the formation of the shape of the SEG-Si. Moreover, it was confirmed that the flat shape of the SEG-Si is obtained by adjusting both the Si2H6 flow rates and the growth temperature.