Low-temperature studies of transition metal doped III-V and II-VI compounds carried out over the last decade have demonstrated the unprecedented opportunity offered by these systems for exploring physical phenomena and device concepts in previously unavailable combinations of quantum structures and ferromagnetism in semiconductors. The work proposed here aims at combining and at advancing epitaxial methods, spatially-resolved nano-characterisation tools, and theoretical modelling in order to understand the intricate interplay between carrier localisation, magnetism, and magnetic ion distribution in DMS, and to develop functional DMS structures. To accomplish these goals we will take advantage of two recent breakthroughs in materials engineering. First, the attainment of high-k oxides makes now possible to generate interfacial hole densities up to 10^21 cm-3. We will exploit gated thin layers of DMS phosphides, nitrides, and oxides, in which hole delocalization and thus high temperature ferromagnetism is to be expected under gate bias. Furthermore we will systematically investigate how the Curie temperature of (Ga,Mn)As can be risen above 180 K. Second, the progress in nanoscale chemical analysis has allowed demonstrating that high temperature ferromagnetism of semiconductors results from nanoscale crystallographic or chemical phase separations into regions containing a large concentration of the magnetic constituent. We will elaborate experimentally and theoretically epitaxy and co-doping protocols for controlling the self-organised growth of magnetic nanostructures, utilizing broadly synchrotron radiation and nanoscopic characterisation tools. The established methods will allow us to obtain on demand either magnetic nano-dots or magnetic nano-columns embedded in a semiconductor host, for which we predict, and will demonstrate, ground-breaking functionalities. We will also assess reports on the possibility of high-temperature ferromagnetism without magnetic ions.