A method for manufacturing regions having adjustable uniform doping in silicon crystal wafers by neutron irradiation according to the reaction Si.sup.30 (n,.gamma.) Si.sup.31 .beta..sup.- P.sup.31 includes the steps of covering the silicon crystal wafer with neutron-absorbing materials of different thicknesses during the irradiation, and selecting materials having isotopes having a high absorption cross-section which yield stable isotopes in the nuclear reaction having small or short-lived activity. Suitable isotopes are B.sup.10, Cd.sup.113, Sm.sup.149, Gd.sup.155 and Gd.sup.157. The regions are generated photolithographically. By such specific material selection, very small layer thicknesses can be used and microfine surface zones or areas can be doped with high geometrical precision and large penetration depth. The method is particularly suited for manufacturing power thyristors.