A semiconductor device having on top of each other in the order mentioned at least the following layers: a drain contact, a drift layer being low doped according to a first conductivity type, n or p, a source region layer being highly doped according to said first type, and a source contact, the source contact being on the first side of the drift layer and the drain contact being on the opposite side of the drift layer, said device also comprising a first grid formed by a plurality of first regions being doped according to a second conductivity type being opposite to said first type, located in said drift layer and laterally separated by drift layer portions, said first regions of said first grid having a first spacing selected: (a) to deplete said drift layer portions responsive to a first voltage applied to said first grid; and (b) to form conducting channels of said first type between adjacent said first regions of the first grid and connect the source region layer with the drain contact via the drift layer, the drain contact being located on the opposite side of the drift layer responsive to a second voltage applied to said first grid, the device also comprising a second grid of a construction corresponding to that of the first grid arranged in said drift layer between the first grid and the drain contact at a vertical distance from said first grid, characterized in that said second grid comprises second regions having a second spacing that is greater than the first spacing of the first regions of the first grid. a drain contact, a drift layer being low doped according to a first conductivity type, n or p, a source region layer being highly doped according to said first type, and a source contact, the source contact being on the first side of the drift layer and the drain contact being on the opposite side of the drift layer, said device also comprising a first grid formed by a plurality of first regions being doped according to a second conductivity type being opposite to said first type, located in said drift layer and laterally separated by drift layer portions, said first regions of said first grid having a first spacing selected: (a) to deplete said drift layer portions responsive to a first voltage applied to said first grid; and (b) to form conducting channels of said first type between adjacent said first regions of the first grid and connect the source region layer with the drain contact via the drift layer, the drain contact being located on the opposite side of the drift layer responsive to a second voltage applied to said first grid, (a) to deplete said drift layer portions responsive to a first voltage applied to said first grid; and (b) to form conducting channels of said first type between adjacent said first regions of the first grid and connect the source region layer with the drain contact via the drift layer, the drain contact being located on the opposite side of the drift layer responsive to a second voltage applied to said first grid, the device also comprising a second grid of a construction corresponding to that of the first grid arranged in said drift layer between the first grid and the drain contact at a vertical distance from said first grid, characterized in that said second grid comprises second regions having a second spacing that is greater than the first spacing of the first regions of the first grid.