An isolation layer having a first depth is formed from an upper face of a substrate. Source/drain regions including junctions are formed in the substrate. Each of the junctions has a second depth substantially smaller than the first depth. A first recess is formed in the substrate by a first etching process. A protection layer pattern is formed on a sidewall of the first recess. A second recess is formed beneath the first recess. The second recess has a width substantially larger than that of the first recess. The second recess is formed by a second etching process using an etching gas containing an SF6 gas, a Cl2 gas and an O2 gas. A gate insulation layer is formed on surfaces of the first and the second recesses. The second recess having an enlarged shape may reduce a width of the junction between the gate electrode and the isolation layer so that a leakage current generated through the junction may decrease.