Bipolartransistor, Halbleitereinrichtung mit einem Bipolartransistor und Verfahren zum Herstellen derselben

An n-type epitaxial layer is formed on a main surface of a p-type silicon substrate. An n-type buried diffusion layer is formed extending in both the p-type silicon substrate and the n-type epitaxial layer. An n-type diffusion layer is formed in the surface of the n-type epitaxial layer, which is disposed above the n-type buried diffusion layer. A p-type diffusion layer is formed so as to surround side ends of the n-type diffusion layer. A p-type buried diffusion layer is formed so as to have a bottom face within the n-type buried diffusion layer and have side ends thereof inside side ends of the p-type diffusion layer. A collector region of a vertical pnp bipolar transistor consists of the p-type buried diffusion layer and the p-type diffusion layer. A p-type diffusion layer, which serves as an emitter region of the pnp bipolar transistor, is formed in the surface of the n-type diffusion layer. Thus, a semiconductor device having a vertical pnp bipolar transistor can be obtained which is capable of reducing its manufacturing cost and improving its reliability.