Lanthanide-incorporated metal nitride (lanthanide-MNx) is investigated as a novel n-type metal gate electrode with tunable work function and good thermal stability for the first time. By incorporating lanthanide elements, such as terbium (Tb), erbium (Er), or ytterbium (Yb), into metal nitride gates, such as TaN and HfN, the work function of MNx can be continuously tuned down to 4.2-4.3 eV even after 1000°C RTA by varying the lanthanide concentrations. In addition, the lanthanide-MNx gates exhibit good thermal stability up to 1000°C on both SiO2 and high-k HfAlO. Possible mechanism for the stability of these metal gates is also discussed and the results show that the enhancement of the nitrogen content in lanthanide-MNx films could be responsible.