A structure and a process for fabricating a bipolar junction transistor (BJT) that is compatible with the fabrication of a vertical MOSFET is disclosed. In the process, at least three layers of material are formed sequentially on a semiconductor substrate, where the substrate includes a buried collector region for the BJT and a source region for the MOSFET. After the at least three layers are formed on the substrate, two windows or trenches are formed in the layers. The first window terminates at the surface of the silicon substrate where the source region has been formed; the second window terminates at the buried collector region. Both windows are then filled with semiconductor material. For the BJT, the bottom portion of the window is filled with material of a conductivity type matching the conductivity of the buried collector, while the upper region of the semiconductor material is doped the opposite conductivity to form the BJT base. Subsequent processing forms the emitter overlying the base and a MOSFET drain overlying the channel formed within the window. The second layer of the three layers is sacrificial and is completely removed. Upon removal of the sacrificial layer, the channel is exposed and a dielectric layer is grown over the exposed channel region, followed by an overlying gate to complete formation of the BJT.