  We studied electrical transport in magnetic semiconductors, which is
determined by scattering of free carriers off localized magnetic moments. We
calculated the scattering time and the mobility of the majority and
minority-spin carriers with both the effects of thermal spin fluctuations and
of spatial disorder of magnetic atoms taken into account. These are responsible
for the magnetic-field dependence of electrical resistivity. Namely, the
application of the external magnetic field suppresses the thermodynamic spin
fluctuations thus promoting negative magnetoresistance. Simultaneously,
scattering off the built-in spatial fluctuations of the atomic spin
concentrations may increase with the magnetic field. The latter effect is due
to the growth of the magnitude of random local Zeeman splittings with the
magnetic field. It promotes positive magnetoresistance. We discuss the role of
the above effects on magnetoresistance of non-degenerate semiconductors where
magnetic impurities are electrically active or neutral.
