Thermal‐neutron transmutation doping of silicon produces phosphorus donors by the nuclear reaction30Si(n,&ggr;)31Si →31P+&bgr;−. Nearly exact compensation of residual impurities in float‐zone silicon is possible with careful monitoring of the neutron fluence. To achieve this goal, an understanding of the dependence on neutron fluence of the various room‐temperature semiconductor electrical parameters is required. An analysis of the fluence dependence of resistivity, Hall coefficient, mobility, and carrier concentration is presented.