Methods of forming a pattern using photoresist compositions

A method of forming a pattern and a photoresist composition, the method including forming a photoresist film on a substrate by coating a photoresist composition thereon, the photoresist composition including a polymerized photoresist additive, a polymer including an acid-labile protective group at a side chain, a photoacid generator, and a solvent; exposing the photoresist film; and forming a photoresist pattern by developing the photoresist film using an aqueous alkali developer, wherein the polymerized photoresist additive includes a hydrophilic repeating unit having an aliphatic hydrocarbon backbone and a side chain containing an oxygen heteroatom in a heterocyclic ring substituted with at least three hydroxyl groups, and a hydrophobic repeating unit having an aliphatic hydrocarbon backbone and a side chain containing a fluorinated aliphatic hydrocarbon group.