A semiconductor device is disclosed. The semiconductor device includes a substrate, a well, an oxidation layer, a gate electrode and a shared source/drain electrode. The substrate has a first surface and a second surface opposite to each other. The well is formed in the substrate. The substrate and the well have a first conductivity type and a second conductivity type respectively. The oxidation layer is formed in the well. The gate electrode is formed above the first surface and has a first opening. The shared source/drain electrode is formed near the first surface in the oxidation layer and exposed from the first opening. The shared source/drain electrode has the first conductivity type.