Germanium as a replacement for Silicon in MOS devices, offers a higher electron (2x) and hole (4x) mobility than Si. A Ge channel MOS technology has been expected to be implemented into future high-speed Si platform, because of the enhanced carrier transport. The poor quality of the native oxide (GeO2) however hampered the use of this material in large scale production. One potential solution is the use of Rare-earth oxides (REOs) such as CeO2, La2O3, Dy2O3, Gd2O3, which can be directly deposited on Ge-substrates. The reliability characteristics of these CMOS devices on Ge-substrates are of important concerns and the main subject of this book. Reliability characteristics such as Charge trapping, SILC, defects generation, dielectrics degradation, polarization relaxation and several other issues are addressed here. A pertinent finding is discussed in this book that it shows Maxwell-Wagner instabilities (that is charge accumulation at the interface of two dielectrics). The gate stacks devices show initially dielectric relaxation effects followed by charge trapping that finally reaches dielectric breakdown. As a matter of fact, the gate stack itself is the cause of charge trapping.