Double diffused field effect transistor having reduced on-resistance

A method of forming a double diffused field effect transistor, said method comprising:

• providing a heavily doped substrate of a first conductivity type;
• introducing at least two dopant species of said first conductivity type into a surface of the substrate so that the substrate has a nonuniform doping profile, said two dopant species consisting of one fast diffusing species and one slow diffusing species;
• forming an epitaxial layer of said first conductivity type over said substrate after the step of introducing said at least two dopant species;
• diffusing said at least two dopant species of said first conductivity type into the epitaxial layer to form a first heavily doped region containing both said fast diffusing species and said slow diffusing species and a second heavily doped region containing only one of said fast diffusing species and said slow diffusing species;
• forming one or more body regions of a second conductivity type within said epitaxial layer;
• forming a plurality of source regions of said first conductivity type within said body regions;
• and
• forming a gate region adjacent to said one or more body regions.