Transmutation doping of semiconductors by neutron irradiation is a well known technique, mainly applied to achieve an extremely uniform low level n-doping of large Si crystals via the 30Si (n,γ) 31Si → 31P nuclear reaction. Similar experiments in other semiconductors never gained a comparable importance. In the last years, however, it has been shown that the doping of semiconductors by implanting radioactive isotopes can yield valuable information about the processes occurring during the incorporation of dopant atoms into the lattice as well as the defect-dopant interactions occurring after the decay of the unstable isotope to a daughter isotope with usually different elemental properties. In this contribution, Hall effect measurements carried out so far on implanted radioactive dopants will be reviewed. The specific problems and the potential of the method will be discussed.