A biCMOS integrated circuit is created on a p-type semiconductor substrate on which first an n-type epitaxial layer then a p-type epitaxial layer is grown. NPN and PMOS transistors are formed in n-wells in the p-type epitaxial layer. n.sup.+ buried layers are located below the n-wells at the interface between the substrate and the n-type epitaxial layer. The n.sup.+ buried layers underlying the n-wells containing NPN transistors are surrounded by p.sup.+ buried layers that extend from the interface between the p-type and n-type epitaxial layers through the n-type epitaxial layers and into the substrate.