Space-charge spectroscopy was employed to study the electronic structure of single and multiple layers of GeSi islands embedded in a n-type Si(001) matrix. For a multilayer sample, the evidence for an electron localization in strained Si in the vicinity of GeSi dots was found. From the admittance measurements the electron binding energy was determined to be 40–70 meV. The electron accumulation was not observed in a sample with a single layer of GeSi islands. Existence of localized electronic states is explained by a modification of the conduction band alignment induced by inhomogeneous tensile strain in Si around the buried GeSi dots.