A semiconductor device includes a buried dielectric layer, a first gate structure, a second gate structure, a first source/drain region, a second source/drain region, a trench, and a contact layer. The first gate structure is disposed on a front-side of the buried dielectric layer, and the second gate structure is disposed on a backside of the buried dielectric layer. The first source/drain region and a second source/drain region are disposed between the first gate structure and the second gate structure. The trench is formed in the buried dielectric layer, and the contact layer is disposed in the trench and electrically coupled to the second source/drain region, where the contact structure and the second gate structure are formed of the same material.