insulation is of no concern the silicon substrate 11 can also be n doped as shown in a preferred embodiment in fig3 a buried layer 22 is produced on a substrate 21 of single crystal silicon which is p doped and has a dopant concentration of 10 15 10 18 cm 3 the n doped buried layer 22 has a dopant concentration of 10 19 10 20 cm 3 this buried layer 22 may be formed epitaxially by implantation or diffusion out of a deposited layer a p doped silicon layer 23 having a dopant concentration of 10 15 10 18 cm 3 is disposed from the buried layer 22 by epitaxy a first highly doped region 24 is disposed in the doped silicon layer 23 for example by implantation this first highly doped region 24 is for example p doped and has a dopant concentration of at least 10 19 cm 3 a second highly doped region 25 is disposed for example by diffusion in the doped silicon layer 23 in a preferred embodiment the second highly doped region 25 annularly surrounds the first highly doped region 24 this second highly doped region 25 is for example n doped and has a concentration of at least 10 19 cm 3 the part of the doped silicon layer 23 displaced between the first highly doped region 24 and the second highly doped region 25 forms a lightly doped region 26 a structured protective layer 27 composed of photoresist for example is disposed at the surface of the highly doped regions 24 25 this structured protective layer 27 leaves the surface of the lightly doped region 26 uncovered also the preferred embodiment of the present invention as shown in fig3 the first highly doped region 24 has a.