Semiconductor device structure and preparation method thereof

The invention relates to a semiconductor device structure and a preparation method thereof. The preparation method of the semiconductor device structure comprises the following steps: providing a substrate; forming an epitaxial layer on the surface of the substrate; forming a buried oxide layer in the epitaxial layer; forming a groove in the epitaxial layer, wherein the buried oxide layer is exposed out of the groove; and forming a gate oxide layer on the side wall of the groove, wherein the gate oxide layer is in contact with the buried oxide layer. The buried oxide layer is formed in the epitaxial layer, then the gate oxide layer is formed on the side wall of the groove, and due to the existence of the buried oxide layer, the problem that the gate oxide layer bears a huge electric field and is broken down during the conduction period of the semiconductor device structure due to the fact that the electric field is gathered at the corner of the bottom of the groove of the semiconductor device structure is sol