Abstract: A semiconductor device (e.g. MOSFET or IGBT) comprises active and termination regions (1,2) formed in a semiconductor substrate (4). The substrate (4) has an upper surface and a termination including a trench (12) extending into the substrate (4) from the upper surface within the termination region (1). Termination trench (12) is at least partly filled with an insulating material (13) which extends from the termination trench (12) to overlie adjacent regions of the device above the surface. A channel stop region (11) extends laterally from a side wall of the termination trench (12) into the substrate (4).