The invention relates to a semiconductor device and a method for manufacturing such a semiconductor device. A semiconductor device according to an embodiment of the invention comprises: a substrate which comprises a base layer, an insulating layer on the base layer, and a semiconductor layer on the insulating layer; and a first transistor and a second transistor formed on the substrate, the first and second transistors being isolated from each other by a trench isolation structure formed in the substrate. Wherein at least a part of the base layer under at least one of the first and second transistors is strained, and the strained part of the base layer is adjacent to the insulating layer. The semiconductor device according to the invention increases the speed of the device and thus improves the performance of the device.