A parasitic PNP bipolar transistor, wherein a base region includes a first and a second region; the first region is formed in an active area, has a depth larger than shallow trench field oxides, and has its bottom laterally extended into the bottom of the shallow trench field oxides on both sides of an active area; the second region is formed in an upper part of the first region and has a higher doping concentration; an N-type and a P-type pseudo buried layer is respectively formed at the bottom of the shallow trench field oxides; a deep hole contact is formed on top of the N-type pseudo buried layer to pick up the base; the P-type pseudo buried layer forms a collector region separated from the active area by a lateral distance; an emitter region is formed by a P-type SiGe epitaxial layer formed on top of the active area.