The degeneration of the metal/HfO2 interfaces for Mo, Ni, and Pd gate metals was studied in this paper. An unstable PdOx interfacial layer formed at the Pd/HfO2 interface, inducing the oxygen segregation for the Pd/HfO2/InGaAs metal oxide capacitor (MOSCAP). The low dissociation energy for the Pd-O bond was the reason for oxygen segregation. The PdOx layer contains O2- and OH- ions which are mobile during thermal annealing and electrical stress test. The phenomenon was not observed for the (Mo, Ni)/HfO2/InGaAs MOSCAPs. The results provide the guidance for choosing the proper metal electrode for the InGaAs based MOSFET.