Properties of the ferromagnetic III-V semiconductor (Ga,Mn)As and heterostructures based on it are reviewed. A model based on hole-mediated ferromagnetic interaction is shown to successfully describe the ferromagnetic transition temperature of (Ga,Mn)As. Spontaneous splitting of resonant tunneling spectra was compared with theory and shown to result from the spin splitting of the valence band. The first demonstration of spin-dependent scattering in magnetic semiconductor trilayers as well as electrical spin injection is also reviewed.