We have developed a base-sensitive silicone resin tethering phenylsulfonylethyl units as base-amplifying groups showing high thermal stability. The resin underwent a base proliferation reaction autocatalytically to generate amino groups on its side chains, which accelerated the base-catalyzed hydrolytic condensation of residual ethoxysilyl units in its main chain. Furthermore, a film of the resin sensitized with a photobase generator provided a negative-working photoimaging material with a high sensitivity.