The transistor includes a second doped region (2) of second conductivity extending from the first surface (14a) into the first doped region (1), while a third doped region (3) of first conductivity extends from the first surface into the second doped region. In the second region is located a channel forming region (4), reaching up to the first surface. On the first surface is deposited a dielectric gate film (5) to cover the channel region. A section of a gate electrode (6) lies opposite to the channel region. Forward biassing members (12) apply a forward biassing voltage to a pn-junction between the second and third doped regions during conductive state. A fourth doped region (10) of second conductivity extends from the second surface (14b) into the semiconductor substrate.
