Si-island growth on a Si(111)-7 x 7 surface was studied at 350 degrees C in situ using high-temperature scanning tunneling microscopy. At the beginning of growth, deposited Si atoms formed small amorphous clusters within each triangular subunit of the 7 x 7 structure. The amorphous clusters grew, and crystallized islands also appeared as the quantity of deposited Si atoms increased. At the domain boundaries of the 7 x 7 structure, islands tended to begin forming on the unfaulted half of the 7 x 7 structure. These phenomena indicate that cancellation of the stacking fault on the substrate surface dominates island growth.