PURPOSE:To obtain a semiconductor unit whose switching rate is slow, by adhering a lifetime killer metal layer to a semiconductor wafer, by removing the remaining layer by polishing after heating for diffusion into the wafer and then rapid cooling, and by gradually cooling the wafer. CONSTITUTION:On N+-type Si wafer 1, N-type layer 2 is formed by epitaxial growth, the entire surface is covered with oxidized film 3, and window hole 4 is made. Next, P-type impurities are diffused from this window hole 4 to form P-type region 5 and Au layer 11 is adhered to the reverse surface of wafer 1. Next, the substrate is heated for 30 to 60 minutes in a neutral atmosphere of 1000 to 1100 deg.C in temperature to diffuse Au into wafer 1 and then cooled suddenly at a rate of 1000 to 1100 deg.C per minute. Then, remaining Au layer 11 is removed by polishing or etching and after gradual heating in a neutral atmosphere at a rate of 30 to 60 deg.C per minute down to 1200 deg.C the substrate is held for 20 minutes. Then, gradual heating is carried out at a rate of 30 to 60 deg.C per minute to provide Ag swell electrode 9 onto region 5 via Au layer 6 and Ag electrode 8 onto the reverse surface of wafer 1 via Au Sb layer 7.
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