The embodiments of the present invention provide a Ge-based NMOS device structure and a method for fabricating the same. By using the method, double dielectric layers of germanium oxide (GeO2) and metal oxide are deposited between the source/drain region and the substrate. The present invention not only reduces the electron Schottky barrier height of metal/Ge contact, but also improves the current switching ratio of the Ge-based Schottky and therefore, it will improve the performance of the Ge-based Schottky NMOS transistor. In addition, the fabrication process is very easy and completely compatible with the silicon CMOS process. As compared with conventional fabrication method, the Ge-based NMOS device structure and the fabrication method in the present invention can easily and effectively improve the performance of the Ge-based Schottky NMOS transistor.