A method of manufacturing a semiconductor device is provided. The method includes forming a first recess partially through a substrate from a first side of the substrate, forming a dielectric layer in the first recess, forming a second recess partially through the dielectric layer from the first side of the substrate, and forming a buried power rail (BPR) in the second recess of the dielectric layer. The method also includes thinning the substrate from a second side of the substrate to a level of the dielectric layer, the second side of the substrate being opposite to the first side of the substrate.