High‐resolution synchrotron radiation photoemission has been used to examine the oxidation states of Si atoms near the Si/SiO2interface. The quality of the starting Si surfaces was intentionally varied and oxidation was done with pure O2and with a mixture of O2plus Cl2. The distribution of intermediate oxidation states and the interface thickness was unaffected by Cl2exposure for atomically flat, well‐ordered Si(100) or (111) surfaces. However, for disordered Si surfaces the presence of Cl2in the oxidizing gas reduced the concentration of Si1+and Si2+species by a factor of 2, indicating a tendency to produce better interfaces. In all cases, Cl was present near the SiO2/Si interface, bonded to Si, and in solution with SiO2as Cl2.