A semiconductor device and a method for forming the same are disclosed. In a method for forming the semiconductor substrate including a cell region and a peripheral region, a guard pattern defined by an epitaxial growth layer located at the edge part between the cell region and the peripheral region is formed. As the guard pattern is not damaged by an oxidation process, a bias leakage path between an N-well bias and a P-well bias of the peripheral region is prevented from occurring Reliability of a gate oxide film may be increased, resulting in an increased production yield of the semiconductor device and implementation of stable voltage and current characteristics.