The interface formation between MgO dielectric layers and the atomically clean and selenium-passivated Ge(100) surfaces has been studied using high-resolution synchrotron radiation based photoemission spectroscopy. Atomically clean germanium was prepared by argon ion bombardment and sub- sequent annealing at 550 °C. MgO deposition on this surface resulted in interface oxide formation whereas no oxidation states were observed for a selenium-treated germanium surface indicating the effectiveness of this interlayer at producing an abrupt MgO/Ge(100) interface. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) In this Letter, the interface formation between MgO dielectric layers and the atomically clean and selenium-passivated Ge(100) surfaces has been studied using high-resolution synchrotron radiation based soft X-ray photoelectron spectroscopy. The Ge 3d spectra acquired at 60 eV for the MgO/Se/Ge sample show the effectiveness of selenium passivated germanium surface at preventing interfacial oxidation during MgO deposition. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.