Gallium manganese arsenide is a magnetic semiconductor. It is based on the world's second favorite semiconductor, GaAs, and as such is readily compatible with existing semiconductor technologies. Differently from other dilute magnetic semiconductors (DMSs), such as the majority of those based on II-VI semiconductors, it is not paramagnetic but ferromagnetic, and hence exhibits hysteretic magnetization behavior. This memory effect is of importance for the creation of persistent devices. In (Ga,Mn)As, the manganese atoms provide a magnetic moment, and each also acts as an acceptor, making it a p-type material. The presence of carriers allows the material to be used for spin-polarized currents. In contrast, many other ferromagnetic DMSs are strongly insulating and so do not possess free carriers. (Ga,Mn)As is therefore a candidate as a spintronic material.