An S/D region including a first region and a second region is provided. The first region is located, with at least a partial thickness, in the substrate. The second region is formed on the first region and made of a material different from that of the first region. A method for forming an S/D region is further provided, and the method includes: forming trenches at both sides of a gate stack structure in a substrate; forming a first semiconductor layer, wherein at least a part of the first semiconductor layer is filled into the trenches; and forming a second semiconductor layer on the first semiconductor layer, wherein the second semiconductor layer is made of a material different from that of the first semiconductor layer. A contact hole and a forming method thereof are also provided which may increase the contact area between a contact hole and a contact region, and reduce the contact resistance.