The state of the surface of standard phosphorus-doped n-Si(111) and n-Si(100) (KEF grade) and boron-doped p-Si(111) (KDB grade) single-crystal wafers treated in a 50% HF–70% HNO3 (1: 3, v/v) polishing solution has been studied using soft X-ray reflection spectroscopy. The fine structure of the reflection spectra in the region of the Si L2,3 ionization threshold has been analyzed. The dependence of the natural oxide thickness on the orientation of a silicon single crystal surface is established.