In a method of manufacturing a semiconductor device, a conductive layer pattern may be formed on a substrate. An oxide layer may be formed on the substrate to cover the conductive layer pattern. A diffusion barrier layer may be formed by treating the oxide layer to increase an energy required for a diffusion of impurities. An impurity region may be formed on the substrate by implanting impurities into the conductive layer pattern and a portion of the substrate adjacent to the conductive layer pattern, through the diffusion barrier. The impurities in the conductive layer pattern and the impurity region may be prevented or reduced from diffusing, and therefore, the semiconductor device may have improved performance.