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Abstract: Germanium quantum dots (QDs) were extracted from ultrathin Si x Ge1−x oxide films using scanning tunneling microscope (STM) tips. The extraction was most efficiently performed at a positive sample bias voltage of +5.0V. The tunneling current dependence of the extraction efficiency was explained by the electric field evaporation transfer mechanism for positive Ge ions from QDs to STM tips. Ge QDs (∼7nm) were formed and isolated spatially by extracting the surrounding Ge QDs with an ultrahigh density of >1012 cm−2. Scanning tunneling spectroscopy of the spatially-isolated QDs revealed that QDs with an ultrahigh density are electrically-isolated from the adjacent dots. [Copyright &y& Elsevier]