In this paper, a study on atomic layer deposited (HfO2)(x)(Al2O3)(1-x) is reported, including the band alignment of (Hfo(2))(x)(Al2O3)(1-x) to (100)Si substrate and thermal stability of (Hfo(2))(x)(Al2O3)(1-x). X-ray photoelectron spectroscopy (XPS) shows that the valence band spectra and O1s energy loss spectra change continuously with the variation of Hf (Al) composition in (HfO2)(x)(Al2O3)(1-x). The energy gap of (HfO2)(x)(Al2O3)(1-x), the valence band offset and the conduction band offset between (HfO2)(x)(Al2O3)(1-x) and the Si substrate as functions of x are obtained based on the XPS results. The thermal stability of Hf alurninates and its impact on oxygen diffusivity through Hf aluminates are also studied by TEM and XPS. Our results demonstrate that both the thermal stability and the resistance to oxygen diffusion of HfO2 are improved by adding Al to form Hf aluminates. (C) 2004 Elsevier B.V. All rights reserved.