Band-gap states of tungsten in silicon carbide ͑polytypes 4H, 6H, and 15R͒ are investigated by deep-level transient spectroscopy ͑DLTS͒ and admittance spectroscopy on n-type SiC. Doping with W is done by ion implantation and annealing. To establish a definite chemical identification of band-gap states, the radioactive isotope 178 W is used as a tracer: band-gap states involving a 178 W isotope are uniquely identified by their decreasing concentration during the nuclear transmutation of 178 W to Hf. In addition, conventional doping studies with stable W isotopes are performed. Within the part of the band gap accessible by DLTS on n-type SiC, there is one tungsten-related deep level with a large capture cross section (10 Ϫ12 cm 2 ) for electrons. In the polytypes 4H, 6H, and 15R, its energy is 1.43, 1.16, and 1.14 eV below the conduction-band edge (E C ), respectively. The polytype dependence of this level position directly reflects the conduction-band offset. In the 4H polytype, an additional level close to the conduction band (E C Ϫ0.17 eV) exists that is absent in the other polytypes because of their smaller band gap. Due to the acceptorlike deep band-gap state, tungsten is a good candidate for a compensating center to produce semi-insulating SiC.