A method of forming a pattern and a negative-type photoresist composition, the method including forming a photoresist film on a substrate by coating a photoresist composition thereon, the photoresist composition including a polymer, a photoacid generator, and a solvent, wherein the polymer includes an alkoxysilyl group as a side chain and is cross-linkable by an acid to be insoluble in a developer; curing a first portion of the photoresist film by exposing the first portion to light, the exposed first portion being cured by a cross-linking reaction of the alkoxysilyl groups therein; and providing a developer to the photoresist film to remove a second portion of the photoresist film that is not exposed to light, thereby forming a photoresist pattern on the substrate.