A chip includes a semiconductor substrate, a well region in the semiconductor substrate, and a Dynamic Threshold Metal-Oxide Semiconductor (DTMOS) transistor formed at a front side of the semiconductor substrate. The DTMOS transistor includes a gate electrode, and a source/drain region adjacent to the gate electrode. The source/drain region is disposed in the well region. A well pickup region is in the well region, and the well pickup region is at a back side of the semiconductor substrate. The well pickup region is electrically connected to the gate electrode.