Surface modification during oxygen plasma etching of polysilylmethylstyrene resists has been monitored using x‐ray photoelectron spectroscopy. Plasma exposure converted the silicon present in the polymers to an oxidized surface region which prevented further chemical etching. Conversion was more rapid and more complete when etching under conditions where higher energy ion bombardment occurred. Polysilylmethylstyrene reached a steady‐state oxide thickness between 3.4 and 5.8 nm, depending on etching conditions. A copolymer of this material with chloromethylstyrene showed a comparable thickness when etched at high ion energies, but did not reach a steady state when etched at conditions where the average ion energy was below 110 eV.