Abstract: Disclosed is an improved bipolar-and-complementary MOS transistor coexisting semiconductor device and a method of making the same. A collector-and-base separator is formed on the site allotted to a bipolar transistor along with a source-and-drain separator on each site allotted to PMOS and NMOS transistors. The superficial collector-and-base separator coating causes no stress to the lattice of the underlying region in the epitaxy of the semiconductor substrate, and therefore there can be no lattice defect which may appear in a conventional composite type semiconductor device structure as a result of selective oxidization of the epitaxial layer to separate the base and collector region of the bipolar transistor. Such a superficial collector-and-base separator according to the present invention assures that the bipolar transistor each of such composite type semiconductor devices is free from the lowering of the breakdown voltage at its collector-and-base junction.