Research on diluted magnetic semiconductors (DMS) has generated great interest for their potential application of semiconductors-based magnetic elements. Ferromagnetic (FM) semiconductors simultaneously exhibit semiconducting properties and spontaneous long-range FM order. The coexistence of these properties in a single material provides fertile ground for both fundamental studies and industrial applications. However, device applications have languished because of low magnetic ordering (Curie) temperature and the inability to incorporate these materials in conventional semiconductor material device. In this context, we have focused our study on structural and magnetic properties of MnxGe1−x DMS layers grown by molecular beam epitaxy on semiconducting Ge(1 1 1) substrate. Mn has been incorporated with increasing concentration from x = 0.02 to 0.1. Their structure has been characterized by transmission electron microscope using both conventional imaging and electronic diffraction. Ge–Mn alloy clusters have been clearly observed for the highest Mn concentration, and alloy phase identified. These observations were completed by classic SQUID magnetometry measurements. We will evidence a critical concentration of Ge above which precipitates of Ge3Mn5 form, enhancing the FM signal in the layer.