The surface structures of 7°, 3.5°, and 2.5° vicinal Si(100) samples tilted about [011̄] have been studied with low-energy electron diffraction. Double-atomic-height steps can be formed on these surfaces after sufficient heat treatment. Angular profile analysis of the integral-order diffracted beams is used to determine step height, average terrace size, terrace size distribution, and degree of step edge roughness. Angular profile analysis of the fractional-order diffracted beams is used to determine the relative fraction of single-atomic-height steps and to measure the degree of correlation in the (2×1) dimer row shifts. The latter is seen as a splitting in the (2×1) beam that is one-half the splitting distance in the (00) beam. This splitting is observed to be reversible with temperature, indicating a phase transition in the configuration of (2×1) dimer row shifts.