High voltage power MOSFET having low on-resistance

A power MOSFET, comprising:

• a substrate of a first conductivity type;
• an epitaxial layer on the substrate, said epitaxial layer having a first conductivity type;
• first and second body regions located in the epitaxial layer defining a drift region therebetween, said body regions having a second conductivity type;
• first and second source regions of the first conductivity type respectively located in the first and second body regions;
• and
• a plurality of trenches located below said body regions in said drift region of the epitaxial layer, said trenches being filled with a material having a dopant of the second conductivity type, said trenches extending toward the substrate from the first and second body regions, said dopant being introduced into sidewalls of the trenches by diffusion, and, being diffused from the material filling said trenches into portions of the epitaxial layer adjacent the trenches.