Trench semiconductor devices

A semiconductor device comprising a semiconductor body in which a p-n junction is formed between a first device region of one conductivity type and an underlying voltage-sustaining zone, wherein a trenched field-shaping region extends in a trench through the voltage-sustaining zone to an underlying second device region, the trench extends from an upper surface of the body through the first device region and the voltage-sustaining zone, the trench accommodates a resistive path of semi-insulating material that is connected between the second device region and a device electrode that contacts the first device region, the resistive path starting below the level of the upper surface of the body, an insulating layer is present at side-walls of the trench to dielectrically couple potential from the resistive path to the voltage-sustaining zone, the first device region extending laterally to the insulating layer, and the voltage-sustaining zone is so dimensioned and doped between the trenched field-shaping regions as to be depleted of free charge carriers between the trenched field-shaping regions in a voltage-blocking mode of operation of the device by the spread of a depletion layer from the p-n junction, the device being characterized in that the insulating layer extends at the side-walls of the trench to an upper level that is higher than a lower level at which the resistive path starts in the trench, which lower level is more closely aligned to the depth of the p-n junction in the body and is protected by the insulating layer, and in that the semi-insulating material extends to the upper level in the trench but is highly doped with conductive dopant between the upper and lower levels so as to form a terminal region of the resistive path, and in that the device electrode that contacts the first device region also contacts this terminal region of the resistive path.