Impurities are formed in the active region of a semiconductor substrate by diffusion from a gate electrode sidewall spacer. A gate electrode is formed on a semiconductor substrate with a gate dielectric layer therebetween. Sidewall spacers are formed on the side surfaces of the gate electrode. Dopant atoms are subsequently introduce to transform the spacers into solid dopant sources. Dopant atoms are diffused from the spacers into the semiconductor substrate to form first doped regions.