本发明提供了一种金属氧化物半导体设备，包含一基底、一闸极结构、一磊晶设备以及一源极/汲极区。闸极结构，设置在该基底上。磊晶结构，设置在该闸极结构两侧的该基底中，其中该磊晶结构包含：一第一缓冲层，为一未掺杂缓冲层，包含一底面部分以及一侧面部分，其中底面部分设置在磊晶结构的一底面上，侧面部分设置在磊晶结构的一凸侧壁上、一磊晶层，为一应力层，被该第一缓冲层包围、以及一半导体层，设置在第一缓冲层与磊晶层之间。源极/汲极区，设置在该磊晶结构中。

The present invention provides a metal oxide semiconductor (MOS) device, including a substrate, a gate structure on the substrate and a source/drain region disposed in the substrate at one side of the gate structure and in at least a part of an epitaxial structure, wherein the epitaxial structure includes a first buffer layer, which is an un-doped buffer layer, including a bottom portion disposed on a bottom surface of the epitaxial structure and a sidewall portion disposed on a concave sidewall of the epitaxial structure, an epitaxial layer which is encompassed by the first buffer layer, and a semiconductor layer which is disposed between the first buffer layer and the epitaxial layer. The source/drain region is disposed in the epitaxial structure.