The electrical activity of Ge dangling bonds is investigated at the interface between GeO 2-passivated Ge (1 1 1) substrate and Al 2 O 3 grown by atomic layer deposition, by means of electrically detected magnetic resonance spectroscopy (EDMR). The Al 2 O 3/GeO 2/Ge stacked structure is promising as a mobility booster for the post-Si future electronic devices. EDMR proved to be useful in characterizing interface defects, even at the very low concentrations of state-of-the-art devices (< 10 10 cm− 2). In particular, it is shown that capping the GeO 2-passivated Ge (1 1 1) with Al 2 O 3 has no impact on the microstructure of the Ge dangling bond.