Abstract: This invention published a parasitic vertical PNP bipolar transistor in BiCMOS (Bipolar Complementary Metal Oxide Semiconductor) process; the bipolar transistor comprises a collector, a base and an emitter. Collector is formed by active region with p-type ion implanting layer. It connects a p-type buried layer which formed in the bottom region of STI (Shallow Trench Isolation). The collector terminal connection is through the p-type buried layer and the adjacent active region. The base is formed by active region with n type ion implanting which is on the collector. Its connection is through the original p-type epitaxy layer after converting to n-type. The emitter is formed by the p-type epitaxy layer on the base region with heavy p-type doped. This invention also comprises the fabrication method of this parasitic vertical PNP bipolar in BiCMOS (Bipolar Complementary Metal Oxide Semiconductor) process.