Superjunction power semiconductor device

1. A power semiconductor device comprising:

a semiconductor substrate of one conductivity;

an epitaxial semiconductor body of another conductivity on a surface of said substrate;

a gate trench in said epitaxial semiconductor body;

a drift region of said one conductivity extending from at least the bottom of said trench to said substrate and extending along only a portion of the sidewalls of said gate trench, said drift region of said one conductivity and said epitaxial semiconductor body being in charge balance;

a source region of said one conductivity formed in said epitaxial semiconductor body adjacent said gate trench and spaced from said drift region of said one conductivity by an invertible channel region adjacent said trench;

a source contact in ohmic contact with at least said source region; and

a drain contact in ohmic contact with said substrate, wherein said drift region includes a high resistivity region adjacent said substrate and a low resistivity region adjacent said gate trench.

2. The power semiconductor device of claim 1 , wherein said drift region of said one conductivity extends into said substrate.

3. The power semiconductor body of claim 1 , further comprising an oxide body disposed inside said trench, said oxide body including a gate oxide portion adjacent at least said invertible channel and a thick portion adjacent the drift region; and a gate electrode inside said trench and adjacent said oxide body.

4. The power semiconductor body of claim 1 , further comprising a high conductivity region of said second conductivity formed in said epitaxial silicon body and making ohmic contact with said source contact.

5. The power semiconductor body of claim 3 , wherein said gate electrode is comprised of polysilicon.

6. The power semiconductor body of claim 5 , wherein said polysilicon is N type.

7. The power semiconductor body of claim 1 , wherein said one conductivity type is N type and said another conductivity is P type.