We have proposed the use of YMnO3 as a ferroelectric layer and of Y2O3 as an insulator layer for ferroelectric gate transistor applications. Insertion of the Y2O3 layer at the YMnO3/Si interface significantly improves the crystallinity of the YMnO3 layer. Although we have used [1 1 1]-oriented Y2O3 layers so far, the epitaxially grown Y2O3 films have a potential to improve the ferro electricity of the ferroelectric film. Furthermore, the Y2O3 films have a relatively large dielectric constant (epsilon =14-17), as well as good thermal stability. However, it still remains unknown what the relationship is between dielectric properties and interfacial structure of epitaxial Y2O3/Si films. We have recently succeeded in obtaining epitaxially grown (1 1 1)Y2O3 on (1 1 1)Si surface by pulsed laser deposition method. In this report, the relationship between the crystallinity of the Y2O3 epitaxial film and the dielectric properties is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.