A method of forming an impurity region is provided to prevent a substrate from being damaged by forming a source and drain of an LDD(Lightly Doped Drain) structure with a spacer. A method of forming an impurity region includes the steps of: forming a first pattern with a first line width on a substrate(100); forming a first impurity region(108) with a first impurity concentration on the surface of the substrate by using the first pattern as an ion implantation mask; forming a second pattern(112) with a second line width by etching the first pattern, wherein the second line width is smaller than the first line width; and forming a second impurity region with a second impurity concentration(110) on the surface of the substrate by using the second pattern as an ion implantation mask, wherein the second impurity concentration is thinner than the first impurity concentration.
