A trench JFET, comprising: a substrate comprising a backside drain region and a topside drift region, the backside drain region and the topside drift region being of a first doping type; active cell mesas extending from the topside drift region, wherein the active cell mesas are separated by trenches cut into the topside drift region; source regions at the tops of the mesas, the source regions being of the first doping type; gate regions on the surfaces of the trenches, the gate regions being of a second doping type, the second doping type being the opposite of the first doping type; vertical channel regions (805, 905), the vertical channel regions extending substantially the height of the mesas and being of the first doping type; and mesa core regions, the mesa core regions being of the first doping type and extending from the centers of the mesas, wherein the doping concentration at the center of the mesa core regions is at least ten times lower than that of the topside drift region; wherein: the vertical channel regions (805, 905) extend laterally between the portion of the gate regions on the vertical walls of the trenches and the mesa core regions, the mesa core regions are between 0.1 to 1 μm shallower than the bottom of the vertical channel regions (805, 905), and the peak doping concentration of the vertical channel regions (805, 905) is at least ten times higher than the doping level of the centers of the mesa core regions. a substrate comprising a backside drain region and a topside drift region, the backside drain region and the topside drift region being of a first doping type; active cell mesas extending from the topside drift region, wherein the active cell mesas are separated by trenches cut into the topside drift region; source regions at the tops of the mesas, the source regions being of the first doping type; gate regions on the surfaces of the trenches, the gate regions being of a second doping type, the second doping type being the opposite of the first doping type; vertical channel regions (805, 905), the vertical channel regions extending substantially the height of the mesas and being of the first doping type; and mesa core regions, the mesa core regions being of the first doping type and extending from the centers of the mesas, wherein the doping concentration at the center of the mesa core regions is at least ten times lower than that of the topside drift region; wherein: the vertical channel regions (805, 905) extend laterally between the portion of the gate regions on the vertical walls of the trenches and the mesa core regions, the mesa core regions are between 0.1 to 1 μm shallower than the bottom of the vertical channel regions (805, 905), and the peak doping concentration of the vertical channel regions (805, 905) is at least ten times higher than the doping level of the centers of the mesa core regions. the vertical channel regions (805, 905) extend laterally between the portion of the gate regions on the vertical walls of the trenches and the mesa core regions, the mesa core regions are between 0.1 to 1 μm shallower than the bottom of the vertical channel regions (805, 905), and the peak doping concentration of the vertical channel regions (805, 905) is at least ten times higher than the doping level of the centers of the mesa core regions.