Electronic device comprising a trench gate field effect device

An electronic device comprising a trench gate field effect device, comprising a semiconductor body having first and second opposed major surfaces, a trench extending into the first major surface so as to define at the first major surface a regular array of polygonal source cells each bounded by the trench, each polygonal source cell containing a source region and a body region with the body regions separating the source regions from a common further region, and a gate extending within and along said trench for controlling a conduction channel through each of the body regions between the corresponding source region and the further region, each polygonal source cell containing a central semiconductor region which is more highly doped than said body regions and which is of opposite conductivity type to the further region and forms a diode with the further region, characterised in that, for each polygonal source cell, said trench defines an inner trench boundary and an outer polygonal trench boundary with the inner trench boundary bounding a central subsidiary cell containing the central semiconductor region, the trench having a plurality of trench portions radiating outwardly from the inner trench boundary to the outer trench boundary and separating the area between the inner and outer trench boundaries into a plurality of segments such that each segment has a boundary with a plurality of sides provided by the trench with at least one side longer than at least one other, each segment forming a subsidiary source cell having a subsidiary source region and a subsidiary body region with the subsidiary body region providing adjacent the boundary of the segment a conduction channel area through which a conduction channel between the associated subsidiary source region and the further region is controllable by the gate within the trench.