A semiconductor device with reduced contact resistance between a substrate and a plug includes a gate electrode disposed over the substrate, the plug formed over the substrate at both sides of the gate electrode and having a sidewall with a positive slope, a capping layer disposed between the gate electrode and the plug, and a gate hard mask layer whose sidewall disposed over the gate electrode is extended to a top surface of the capping layer. By employing the capping layer having a sidewall with a negative slope, the plug having the sidewall with a positive slope can be formed regardless of a shape or profile of the sidewall of the gate electrode. As a result, the contact area between the substrate and the plug is increased.