The influence of different thermal oxidation/nitridation durations (5, 10, 15, and 20 minutes) at 400°C for transforming metallic Ho sputtered on Ge substrate in N2O gas ambient have been systemically investigated to develop Ho2O3/Ge based on metal-oxide-semiconductor (MOS) device. The structural and chemical properties of the film were characterized using X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy. Cubic-Ho2O3 dielectric layer has been formed along with sandwiched interfacial layer (IL) between substrate Ge and high-k interface comprising tetragonal-GeO2, GeOx, and cubic-Ge3N4 compounds. Energy band alignment for Ho2O3/IL/Ge MOS stack has been determined from XPS spectrum where 10-minute sample exhibited maximum conduction band offset, �Ec ~ 2.47 eV and valance band offset, �Ev ~ 4.67 eV, inducing lower leakage current density, J ~ 10�5 A cm�2 at the higher electrical breakdown, EBD ~ 8.59 MV cm�1. The electrical results of this sample also revealed higher dielectric constant k ~ 13.60, lowest effective oxide charge, slow trap density, and interface trap density which has been attributed to the confinement of Ho2O3 dielectric interface and densification Ge3N4 interfacial compound. An oxidation/nitridation model related to Ho2O3/IL/Ge stack growth is being proposed. It has been anticipated that Ho2O3 could serve as a gate dielectric oxide for Ge-based MOS systems such as a capacitor. © 2021 John Wiley & Sons Ltd.