Abstract: A heater unit manufacturing method constituted by the steps of: forming multitudes of inorganic fibers into a heat insulating housing block through molding; heat treating the heat insulating housing block after impregnating the block with heat resistant resin; and mounting a heating element inside of the heat treated heat insulating housing block.

Abstract: A surge absorption device includes fundamentally a first semiconductor region, a second semiconductor region forming a pn junction between itself and the first region, a third region determining the effective thickness of the second region, and a fourth region provided in contact with the first region and forming an injection junction for causing first minority carriers of a kind the same as that of minority carriers in the first region to be injected into the first region. When a depletion layer formed by application of reverse bias across the pn junction reaches the third region, a punch-through region is formed in the second region. In this state, when minority carriers are injected from the fourth region into the first region, the minority carriers are absorbed by the second region to constitute the device current.