A semiconductor device and a circuit are provided. The semiconductor device includes a substrate, a first gate structure, a first doped region, and a capacitor structure. The substrate includes a first well region having a first conductive type. The first gate structure is disposed on the substrate. The first doped region is in the substrate and has a second conductive type different from the first conductive type. The first gate structure and the first doped region are included in a first transistor. The capacitor structure includes a first electrode electrically coupled to the first doped region. The second doped region is in the substrate and has the second conductive type. The second doped region is electrically coupled to the first electrode of the capacitor structure and the first doped region.