High power mosfet type device

In a high power MOSFET having a plurality of closely packed polygonal sources 123 spaced from one another on one surface of a semiconductor body 121, and an elongated gate electrode 141 exposed in the spacing between the polygonal sources and cooperating with two channels, 161, 162 one for each adjacent source electrode, to control conduction from the source electrode through the channel and then to drain electrode 151 on the opposite surface of the semiconductor body, the conductive region adjacent the channel and between adjacent sources is relatively highly conductive in the section 128 of the channel adjacent to the surface containing the sources. The polygonal shaped source members are preferably hexagonal. Each polygonal region has a relatively deep central portion 122, 123 and a shallow outer shelf portion 124, 125. The shelf portion generally underlies an annular source region 126, 127. The deep central portion underlies an aluminium conductive electrode 150 and is sufficiently deep that it will not be fully penetrated by aluminium spiking. <IMAGE>