A semiconductor transistor device is provided. The semiconductor transistor device includes a semiconductor substrate, a gate structure, a first isolation structure, a first doped region, and a first extra-contact structure. The gate structure is disposed on the semiconductor substrate, and the semiconductor substrate has a first region and a second region respectively located on two opposite sides of the gate structure. The first isolation structure and the first doped region are disposed in the first region of the semiconductor substrate. The first extra-contact structure is disposed on the semiconductor structure. The first extra-contact structure is located between the gate structure and the first doped region and penetrating into the first isolation structure in the first region of the semiconductor substrate, and the first doped region is electrically coupled to the first extra-contact structure.