Structures and methods for integrating a thick oxide high-voltage metal-oxide-semiconductor (MOS) device into a thin oxide silicon-on-insulator (SOI). A method of forming a semiconductor structure includes forming first source and drain regions of a first device below a buried oxide layer of a silicon-on-insulator (SOI) wafer, forming a gate of the first device in a layer of semiconductor material above the buried oxide layer; and forming second source and drain regions of a second device in the layer of semiconductor material above the buried oxide layer.