<p>The present invention relates to a CMOS semiconductor device. The CMOS semiconductor device includes: a first MOS transistor provided in a well of a semiconductor substrate; a second MOS transistor which is adjacent to the first MOS transistor and is provided in the semiconductor substrate; a first guard ring which partly surrounds the first MOS transistor in the well; a second guard ring which partly surrounds the second MOS transistor; a first isolated guard ring; and a second isolated guard ring. The first and second guard rings have open-loop structures.</p>
