A semiconductor device includes a substrate, a well region of a first-conductivity type disposed in the substrate, a first impurity region of a second-conductivity type and having a plurality of branches disposed in the well region, a second impurity region of the first-conductivity type and having a plurality of branches, and a third impurity region of the first-conductivity type disposed in the well region. The second-conductivity type is opposite to the first-conductivity type. A portion of the first impurity region overlaps a portion of the third impurity region. The plurality of branches of the second impurity region are disposed in the third impurity region, and a portion of the third impurity region is disposed between the first impurity region and the second impurity region.