  In a recent Letter, Berciu and Bhatt have presented a mean-field theory of
ferromagnetism in III-V semiconductors doped with manganese, starting from an
impurity band model. We show that this approach gives an unphysically broad
impurity band and is thus not appropriate for (Ga,Mn)As containing 1-5% Mn. We
also point out a microscopically unmotivated sign change in the overlap
integrals in the Letter. Without this sign change, stable ferromagnetism is not
obtained.
