One layer of self-assembled Ge quantum dots with Si barrier were grown on high-resistivity p-type Si(100) substrates by rapid thermal chemical vapor deposition followed by Mn ion implantation and postannealing. A presence of ferromagnetic structure was confirmed in the diluted magnetic quantum dots (DMQDs). The DMQDs through 10 min annealing were found to be homogeneous and to exhibit p-type conductivity, semiconducting property, and ferromagnetic ordering with a Curie temperature, T-C = 170 K. The DMQDs through 60 min annealing were found to be semi-insulating and ferromagnetic ordering with a Curie temperature over 300 K. The X-ray diffraction data show that there is a phase separation of Mn-rich phases Mn5Ge3 from MnGe nanostructure. Temperature-dependent electrical resistivity data indicates that manganese introduces two acceptor levels in germanium at 0.14 or 0.13 eV from the valence band and 0.46 or 0.43 eV from the conduction band, implying that Mn is substituting Ge. Therefore, it is likely that the ferromagnetic exchange coupling of the sample with TC = 170 K is hole-mediated and the ferromagnetism of the sample with T-C > 300 K is due to Mn5Ge3 phase. (c) 2007 The Electrochemical Society.