A semiconductor structure includes a semiconductor substrate having a first electrical portion, a second electrical portion, and a bridged conductive layer. The first electrical portion includes a first semiconductor well, a second semiconductor well in the first semiconductor well, and a third semiconductor well and a fourth semiconductor well in the second semiconductor well. The second electrical portion includes a fifth semiconductor well, a semiconductor layer in the fifth semiconductor well, and a sixth semiconductor well and a seventh semiconductor well in the fifth semiconductor well. The semiconductor layer has separated first and second portions. The bridged conductive layer connects the fourth semiconductor well and the sixth semiconductor well.