A chemically amplified (CA) methacrylate resist containing polyhedral oligosilsesquioxane (POSS) has been synthesized by AIBN-initiated free radical polymerization. While the polymer of low POSS concentrations showed Little improvement in reactive ion etching (RIE) resistance, incorporation of 20.5 wt % of the POSS monomer into methacrylate-based CA resists significantly improved their RIE resistance in the O-2 plasma. High-resolution transmission electron microscopy revealed that the RIE resistance improvement was due to the formation of rectangular crystallite-constituting; networks of the silica cages uniformly distributed within the polymer matrix.