A new silicone‐based negative resist (SNR) for a two‐layer resist system was synthesized by the chloromethylation of oligomeric diphenyl siloxane (ODPS), in which the polymerization of ODPS occurred simultaneously. The molecular weight of SNR could be controlled by the reaction conditions. SNR showed excellent dry etching resistance to RIE owing to the siloxane main chain structure and high sensitivity and high resolution to electron beam, x‐ray, and deep UV radiation due to chloromethyl groups as the crosslinking units. The high glass transition temperature of SNR (150°C) due to diphenyl structure contributes to improving resolution and eliminates lithographic problems involved in low conventional silicone resins. Submicron patterns with a high aspect ratio were fabricated in a two‐layer system comprised of SNR on AZ1350 photoresist bottom layer.