A high voltage MOS transistor comprises a first drain/source region formed over a substrate, a second drain/source region formed over the substrate and a first metal layer formed over the substrate. The first metal layer comprises a first conductor coupled to the first drain/source region through a first metal plug, a second conductor coupled to the second drain/source region through a second metal plug and a plurality of floating metal rings formed between the first conductor and the second conductor. The floating metal rings help to improve the breakdown voltage of the high voltage MOS transistor.