Recent empty-state scanning tunneling microscopy (STM) images of Si(5 5 12)-2 x 1 have shown that this surface consists of four types of one-dimensional structures such as honeycomb (H) chain, pi-bonded (pi) chain, dimer-adatom (D-A) row, and tetramer (T) row. To confirm this revised structural model of the Si(5 5 12)-2 X I surface, the authors performed homoepitaxy on the reconstructed Si(5 5 12) surface held at 550 degrees C and studied the results by STM. Under equilibrium at 550 degrees C there exists three kinds of phases composed of (225), D(337), T(337), and (112) subunits. These subunits consist of only two commutable rows, D-A and T rows, as well as two commutable chains, H and pi chains. Mutual transformations among three phases by means of additional Si atoms are well explained by a new structural model having only two kinds of chains. (C) 2007 American Vacuum Society.