  We show that suitably-designed magnetic semiconductor heterostructures
consisting of Mn delta-doped GaAs and p-type AlGaAs layers, in which the
locally high concentration of magnetic moments of Mn atoms are controllably
overlapped with the 2-dimensional hole gas wavefunction, realized remarkably
high ferromagnetic transition temperatures (TC). Significant reduction of
compensative Mn interstitials by varying the growth sequence of the structures
followed by low temperature annealing led to high TC up to 250 K. The
heterostructure with high TC exhibited peculiar anomalous Hall effect behavior,
whose sign depends on temperature.
