Continued scaling of microelectronic devices is demanding that alternatives to SiO2 as the gate dielectric be developed soon. This in turn has placed enormous pressure on the abilities of physical characterization techniques to address critical issues such as film and interface structure and composition, transport properties, and thermal or chemical stability. This article summarizes the strengths and capabilities of four techniques used for the materials characterization of alternative gate dielectrics: scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), medium-energy ion scattering (MEIS), infrared-absorption spectroscopy (IRAS), and x-ray photoelectron spectroscopy (XPS). The complementary nature of these techniques has allowed for a detailed picture of the various properties of alternative gate dielectrics, and in particular of the dielectric/silicon interface. Critical issues and features of several important alternative gate dielectrics, ZrO2, AI2O3, Y2O3, and Gd2O3, are explored in light of the well-studied SiO2/Si system.