In this report we use vacuum ultraviolet spectroscopic ellipsometry (VUV‐SE) to determine the optical as well as structural properties of high‐k metal oxides, in particular, of hafnium aluminates and titanium aluminates grown by jet‐vapor deposition. In our opinion, the adapted approach employed in this study can be applied in most other high‐k dielectric thin films which are of great interest in developing a new material replacement for the SiO2gate dielectric in CMOS and other IC devices. Specifically, VUV spectroscopic ellipsometry measurements were performed on a commercial ellipsometer with spectral range from 1.0 eV (1240 nm) to 8.7 eV (143 nm). The Generalized Tauc‐Lorentz (GTL) dispersion was used to determine the dielectric functions of these films. An ellipsometric model consisting of two layers of different film densities was found to be in excellent agreement with the experimental data. For the TiAlO films, only one film was needed in the model to fit the data. The optical bandgaps are seen to increase, while the relative film densities decrease, with increasing Al in the films. In addition, the optical dielectric functions shift to higher energy and decrease in magnitude as the films become more insulating. As a result, the Al appears to be mixed at the atomic level instead of forming a phase separation between HfO2and Al2O3. For TiAlO, we observed similar results except that the fundamental optical bandgap was not strongly affected by the amount of Al incorporated in the films. In our opinion, the adapted approach employed in this study can be applied in most other high‐k dielectric thin films which are of great interest in developing a new material replacement for SiO2in CMOS and other IC devices. © 2003 American Institute of Physics