Semiconductor device and manufacturing method thereof

A semiconductor device includes a gate structure, a source/drain epitaxial structure, a front-side interconnection structure, a backside via, an isolation material, and a sidewall spacer. The source/drain epitaxial structure is on a side of the gate structure. The front-side interconnection structure is on a front-side of the source/drain epitaxial structure. The backside via is connected to a backside of the source/drain epitaxial structure. The isolation material is on a side of the backside via and in contact with the gate structure. The sidewall spacer is sandwiched between the backside via and the isolation material. A height of the isolation material is greater than a height of the sidewall spacer.