Abstract: A device includes an array of cells, the source regions of the individual cells comprising a plurality of source region branches each extending towards a source region branch of an adjacent cell, the base regions of the individual cells comprising a corresponding plurality of base region branches merging together to form a single base region surrounding the source regions. The junctions between the merged base region and the drain region define rounded current conduction path areas for the on-state of the device between adjacent cells. Floating voltage regions of opposite conductivity type to the drain region are buried in the substrate beneath the merged base region. The features of the floating voltage regions define rings of the opposite conductivity type to the drain region that surround the current conduction paths of respective cells. The floating voltage regions include respective islands situated within the current conduction paths.