Insulated gate bipolar transistor

An insulated gate bipolar transistor, comprising:

• a drift region of a first conductivity type;
• a body region of a second conductivity type disposed on the drift region;
• a cathode first conductivity-type region disposed within the body region;
• a cathode second conductivity-type region disposed within the body region;
• an anode first conductivity-type region disposed on the drift region, and comprising a first region and a second region;
• and
• an anode second conductivity-type region disposed on the drift region, and comprising a third region and a fourth region;
• wherein a dopant concentration of the first region is less than a dopant concentration of the second region;
• a dopant concentration of the third region is less than a dopant concentration of the fourth region;
• the third region is disposed between the fourth region and the body region;
• the first region is disposed below the fourth region;
• the second region is disposed below the third region and between the first region and the body region;
• and
• the first conductivity type is opposite to the second conductivity type;
• further comprising a field oxygen layer disposed between the body region and the anode second conductivity-type region, wherein a side of the field oxygen layer extends to an edge of the third region and an edge of the second region, and wherein the field oxygen layer covers a portion of a buffer layer.