Methods of fabricating a semiconductor device, and related devices, include forming a gate electrode on a substrate, forming a first buffer layer, a second buffer layer and a third buffer layer on side surfaces of the gate electrode and on the substrate near the gate electrode, forming a spacer covering the side surfaces of the gate electrode on the third buffer layer, the third buffer layer on the substrate being exposed, exposing the second buffer layer on the substrate by removing the exposed third buffer layer, exposing the first buffer layer on the substrate by removing the exposed second buffer layer, forming deep junction in the substrate using the spacer as a mask, and removing the spacer. The third buffer layer is a material layer having a higher dielectric constant than the second buffer layer. The spacer includes a material layer different than the third, second and first buffer layers.