The authors used RHEED to characterize the surface step structure of Si(001) vicinal surfaces tilted from 0.5 to 4° toward the [110] azimuth.The surface of small misorientation (0.5, 1°) after a high-temperature anneal was double-domain with monolayer steps, while that of a large misorientation (4°) was single-domain with bilayer steps.The single-domain structure appeared for all samples during homoepitaxial growth.For surfaces tilted by 0.5 or 1°, the selective growth of the first half of a monolayer was observed which changed the surface from double-domain with monolayer steps to single-domain with bilayer steps.