A semiconductor structure comprising a substrate, an active device, a field oxide layer and a poly-silicon resistor is disclosed. The active device is formed in a surface area of the substrate. The active device has a first doped area, a second doped area and a third doped area. The second doped area is disposed on the first doped area. The first doped area is between the second and the third doped areas. The first doped area has a first type conductivity. The third doped area has a second type conductivity. The first and the second type conductivities are different. The field oxide layer is disposed on a part of the third doped area. The poly-silicon resistor is disposed on the field oxide layer and is electrically connected to the third doped area.