A MOS transistor and a method for fabricating the MOS transistor. The present
invention
enables implementation of a stable semiconductor device that is capable of protecting
against leakage current generation by improving the "LDD effect" and securing a
large process margin by adjusting an "off" current. The method for fabricating
a MOS transistor includes placing or arranging an epitaxial layer between a silicon
wafer and a gate electrode, and forming three impurity regions, including a very
low concentration impurity region, and a low concentration impurity region and
a high concentration impurity region (source and drain region).