The present disclosure provides a method for manufacturing a semiconductor device. The method includes providing a substrate. The substrate comprises a first well region having a first conductive type. The method also includes forming a first gate structure on the substrate. The method further includes forming a first doped region in the substrate. The first doped region 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. In addition, the method includes forming a capacitor structure electrically coupled to the first doped region of the substrate. The method also includes forming a second doped region in the substrate. The second doped region has the second conductive type, the second doped region and the first well region collectively serve a diode, and the second doped region is electrically coupled to the first electrode of the capacitor structure and the first doped region.