Provided is a semiconductor device including a substrate having a P-type conductivity, a buried layer having an N-type conductivity, an NPN bipolar junction transistor (BJT), and a first well region having the P-type conductivity. The buried layer is located on the substrate. The NPN BJT is located on the buried layer. The first well region is located between the buried layer and the NPN BJT. The NPN BJT is separated from the buried layer by the first well region.