Abstract: A SJ power MOSFET having a super junction structure includes a P? pillar layer buried in a drift layer as an N? pillar layer and including a P pillar upper layer and a P pillar lower layer, wherein the P? pillar layer is configured to fulfill the relationships: Db>Da and Ca>Cb, where Da is a defect density of the P pillar upper layer, Ca is an impurity concentration of the P pillar upper layer, Db is a defect density of the P pillar lower layer, and Cb is an impurity concentration of the P pillar lower layer, so as to achieve a higher switching speed and ensure higher breakdown stability.

Abstract: A process for producing a ceramic honeycomb structural body, comprises the steps of placing a green ceramic honeycomb structural body on a ceramic plate, and then firing the green ceramic honeycomb structural body. The green ceramic honeycomb structural body is placed on the ceramic plate in the state that a cell-opened end face contacts the ceramic plate. The ceramic plate is composed mainly of heat-resistive inorganic fibers, and has a bulk density of not less than 1.00 g/cm.sup.3.