A diode structure is provided. The diode structure comprises a first conductive type substrate, a second conductive type first well region, a first conductive type second well region, a second conductive type first doped region, a first conductive type second doped region and a second conductive type third doped region. The first well region is located within the substrate and the second well region is located within the first well region. The first doped region is located within the first well region and detached from the second well region but adjacent to the surface of the substrate. The second doped region and the third doped region are located within the second well region and adjacent to the surface of the substrate. The second doped region is located between the first doped region and the third doped region but detached from both the first doped region and the third doped region.