Poly(phenylhydrosilane) becomes soluble in a 2.38% tetramethylammoniumhydroxide aqueous solution after exposure to UV light. This is the first report that the polysilanes not bearing acidic groups can be developed with dilute basic aqueous solutions. Addition of 3,3’,4,4’-tetra(t-butylperoxycarbonyl)benzophenone increases the resist sensitivity. The reaction mechanism is as follows : PS1 photodecomposes to form silyl compounds having SIGH groups, which become soluble in an aqueous base solution, because these silane compounds bearing SiOHs are acidic.