We review the impact of semiconductor surface preparation on the performance of metal-oxidesemiconductor field-effect transistor (MOSFET) gate stacks. We discuss high-permittivity dielectrics such as hafnium oxide and aluminum oxide on silicon and on the high carrier mobility substrate germanium. On Si, scaling of the gate stack is the prime concern. On Ge, fundamental issues of chemical and electrical passivation need to be resolved. Surface treatments considered include oxidation, nitridation, hydrogenation, chlorination, and organic functionalization.