Annealing-induced interface degradation of (111) Si/SiO2 has been studied in noble gas ambients. A remarkable impeding effect on degradation is found, inversely proportional to the gas atomic diameter. The noble gases physically obstruct SiO removal through their occupation of SiO accessible sites in the oxide, thus impeding degradation. The observed process represents blocking of a chemical reaction by physical action. © 1999 American Institute of Physics.