This article discusses the bonding chemistry of alternative high-k gate dielectrics that have been considered for advanced complementary metal-oxide- semiconductor devices. The replacement of SiO2 by alternative gate dielectrics requires a transition from a thermally deposited native oxide to a deposited gate dielectric. A classification scheme based on bond ionicity separates alternative gate dielectric materials into three groups that are differentiated by their amorphous morphology and electronic structure and properties. This scheme establishes trends between bond ionicity and (i) the average bonding coordination of the constituent atoms, (ii) the thermal stability against chemical phase separation and/or crystallization, and (iii) the dielectric constant. It also provides a framework for the evaluation of different criteria that have been proposed for optimization of alternative high-k metal and transition metal oxides, and their alloys with SiO2 and Al2O3. Based on technology targets for device and wafer performance and reliability, there is as yet no ideal replacement for SiO2 that increases capacitance while at the same time maintaining low levels of interfacial defects.