Photoresist patterns are formed using a photoresist composition, which includes water, a negative photoresist polymer having a salt-type repeating unit, and a photoacid generator, so that a developing process can be performed not by using conventional TMAH solution but by using water. Additionally, because the main solvent of the composition is water, the disclosed photoresist composition is environment-friendly, and has a low light absorbance at 193 nm and 248 nm, which is useful in a photolithography process using a light source in a far ultraviolet region when high-integrated fine circuits of semiconductor device are manufactured.