Selective adsorption of disilane, Si2H6, on the Si(111) surface partially terminated by Ga atoms has been investigated by scanning tunneling microscopy in the temperature range from 390 to 480 °C. When the substrate temperature is below 420 °C, disilane is dissociatively adsorbed in Si(111)7×7 regions, whereas it is hardly adsorbed in Si(111)×-Ga regions due to Ga termination of Si dangling bonds. The migration of precursors dissociated from disilane is not significant on the Si(111)7×7 surface below 420 °C. Consequently, precursors containing Si atoms are not supplied to Ga-terminated regions by the disilane dissociation in the Ga-terminated regions or the surface migration from 7×7 regions. Above 420 °C, precursors dissociated from disilane migrate from Si(111)7×7 regions to Ga-terminated regions, resulting in a two-dimensional island growth of Si in Ga-terminated regions. © 1997 American Vacuum Society.