Bipolar semiconductor device with sub-cathode enhancement regions

An insulated-gate bipolar transistor (IGBT) comprising a plurality of IGBT unit cells, each of said plurality of IGBT unit cells comprising:

• a drift region having a first conductivity type situated over a collector having a second conductivity type opposite said first conductivity type;
• first and second depletion trenches, each having a depletion electrode;
• a first gate trench situated between said first and second depletion trenches, said first gate trench extending into said drift region and being adjacent to emitter diffusions;
• an enhancement region having said first conductivity type localized in said drift region between said first gate trench and at least one of said first and second depletion trenches,
• a third depletion trench adjacent to one of said first and second depletion trenches, wherein said enhancement region does not extend between said third depletion trench and either of said first and second depletion trenches,
• wherein said first gate trench extends deeper into said drift region than said enhancement region.