A parasitic PIN device in a BiCMOS process is disclosed. The device is formed on a silicon substrate, in which an active region is isolated by shallow trenches. The device includes: an N-type region, consisting of N-type pseudo buried layers respectively formed at the bottom of shallow trench isolation oxide layers and extending into the active region; an I-type region, consisting of an N-type collector implantation region formed in the active region and contacting with the N-type region; a P-type region, consisting of a P-doped intrinsic base epitaxial layer on a surface of the active region and contacting with the I-type region. The device of the present invention has a low insertion loss and a high isolation. A manufacturing method of parasitic PIN device in compatible with existing BiCMOS process is also disclosed.