  We investigate the relationship between the Curie temperature TC and the
carrier density p in the ferromagnetic semiconductor (Ga,Mn)As. Carrier
densities are extracted from analysis of the Hall resistance at low
temperatures and high magnetic fields. Results are found to be consistent with
ion channeling measurements when performed on the same samples. We find that
both TC and the electrical conductivity increase monotonically with increasing
p, and take their largest values when p is comparable to the concentration of
substitutional Mn acceptors. This is inconsistent with models in which the
Fermi level is located within a narrow isolated impurity band.
