Surface structures during silicon growth on an Si(111)7X7 surface were investigated by reflection high-energy electron diffraction (RHEED) and scanning tunnelling microscopy (STM). From an analysis of RHEED intensity rocking curves and oscillations, we conclude that a dimer-adatom-stacking fault (DAS) structure with 5X5 periodicity and a metastable pyramidal cluster-type structure are formed on terraces during growth, and a 7X7 DAS structure grows from step edges. From STM observations of isolated silicon islands on Si(111)7X7 at high temperatures, it is found that stable small islands with a 5X5 DAS structure are formed, but 7X7 islands are mostly unstable. Therefore it is believed that the formation of a 5X5 structure during growth is due to the stability of the small islands. In addition, the formation of the metastable structure promotes successive epitaxial growth accompanied by stacking fault dissolution in the dimer-stacking fault framework.