Switching element

A switching element, comprising:

• a semiconductor substrate that has an upper surface on which a trench is disposed;
• a gate insulating film that covers an inner surface of the trench;
• and
• a gate electrode that is disposed inside the trench, the gate electrode being insulated from the semiconductor substrate by the gate insulating film, wherein
• the semiconductor substrate further includes:
• an n-type source region in contact with the gate insulating film on a side of the trench;
• a p-type body region in contact with the gate insulating film on the side below the source region;
• an n-type drift region that is arranged below the body region, the n-type drift region being in contact with the gate insulating film on the side below the body region and with the gate insulating film at a bottom surface of the trench;
• a p-type first electric field reduced region that is arranged inside the drift region below the trench to be spaced away from the bottom surface of the trench, the p-type first electric field reduced region extending along the bottom surface of the trench;
• and
• a p-type connection region that protrudes downward from the body region to reach the first electric field reduced region, the p-type connection region extending in a direction intersecting the trench when viewed in a plan view,
• a permittivity of the connection region is ε (F/cm), a critical electric field strength of the connection region is Ec (V/cm), an elementary charge is e (C), and an area density of p-type impurity when viewed in a plan view of the connection region located below the trench is Q (cm−2), wherein
• Q>ε*Ec/e, and
• a p-type impurity concentration in the connection region is higher than a p-type impurity concentration in the first electric field reduced region.