Semiconductor devices are provided including a gate across an active region of a substrate; a source region and a drain region in the active region on either side of the gate and spaced apart from each other; a main channel impurity region in the active region between the source and drain regions and having a first channel impurity concentration; and a lightly doped channel impurity region in the active region adjacent to the drain region. The lightly doped channel impurity region has the same conductivity type as the main channel impurity region and a second channel impurity concentration, lower than the first channel impurity concentration. The lightly doped channel impurity region and the main channel impurity region contain a first element. The lightly doped channel impurity region also contains a second element, which is a different Group element from the first element.