forming a gate layer on a semiconductor substrate;

implanting low-concentrated impurities into the semiconductor substrate around both sides of the gate layer to form a low-concentrated diffusion region;

forming an inter-level insulation film on an entire surface of the semiconductor substrate on which the low-concentrated diffusion region is formed;

patterning the inter-level insulation film to form contact holes exposing the semiconductor substrate on which the low-concentrated diffusion region is formed;

growing an epitaxial layer on the semiconductor substrate exposed by the contact holes; and

forming a contact pattern to fill the contact holes;

wherein during the growth of the epitaxial layer, impurities are implanted while gradually increasing a concentration of the impurities so that an impurity dopant concentration of the epitaxial layer increases with increasing distance from the semiconductor substrate.