A polymer used for a negative type resist composition having a first repeating unit of a Si-containing monomer unit, a second repeating unit having a hydroxy group or an epoxy ring and copolymerized with the first repeating unit is provided. The first repeating unit is represented by the following formula: ##STR00001## wherein R.sub.1 is a hydrogen atom or a methyl group, X is a C.sub.1 C.sub.4 alkyl or alkoxy group, and n is an integer from 2 to 4. Also, there is provided a negative type resist composition including the polymer which is an alkali soluble base polymer, a photoacid generator and a crosslinking agent cross linkable in the presence of an acid.