Grounded-trench-MOS structure assisted normally-off bipolar-mode power FET

A normally-off bipolar-mode FET having a V/sub DSS/ of 700 V with n/sup +/-n/sup -/-n/sup +/ structure has been developed. The transistor has a new type trench-MOS structure. N/sup +/-source and n/sup -/-channel are sandwiched by deep trench-MOS structures whose potential is fixed to the ground. They act virtually as the gates of a long-channel JFET. The p-gate contacts with every insulating film, which controls the channel conditions by the potential of p-type inversion layer. When the gate is shorted, the channel withstands up to the avalanche condition. Furthermore, it has a V/sub DSO/ of about 400 V.