We propose a novel formation process of a Ge nitride interfacial layer (NIL) and demonstrate successful Ge-nMISFETs operation with NIL, for the first time. We also examine the impact of NIL on the performance of the nMISFETs. It is found that, compared to an oxide interfacial layer (OIL), NIL is quite effective in suppressing the generation of positive fixed charges and electron trapping centers in high-k/Ge gate stacks which degrade the FET performance. By combining NIL with HfO2 deposition, we successfully achieve excellent Ge-nMISFET operations, such as the SS of 74mV/dec. and high electron mobility of 870cm(2)/Vs, compellable to that of Si. This is the highest electron mobility value for Ge(100)-nMISFETs with high-k gate stacks.