Ultra-low drain-source resistance power MOSFET. In accordance with an embodiment of the preset invention, a semiconductor device comprises a plurality of trench power MOSFETs. The plurality of trench power MOSFETs is formed in a second epitaxial layer. The second epitaxial layer is formed adjacent and contiguous to a first epitaxial layer. The first epitaxial layer is formed adjacent and contiguous to a substrate highly doped with red Phosphorus. The novel red Phosphorus doped substrate enables a desirable low drain-source resistance.