PURPOSE: To obtain structure and a manufacturing method of a bipolar IC having a vertical transistor wherein the width of a base region is formed with comparatively high precision, stable characteristics are obtained, and high frequency characteristics are improved.

CONSTITUTION: An n+ type buried layer 12 is formed on the surface of a p-type silicon substrate 11 by thermal diffusion or the like, and a p+ type buried layer 13 is formed on the n+ type buried layer. By epitaxial growth or the like from above the layer 13, an n-type layer 14 is formed for isolation on the whole surface. By boron ion-implantation in the whole part of the n-type layer or in the base region, a p-type layer 16 of low concentration is formed so as to be in contact with the p+ type buried layer. After an n-type base layer 16 of comparatively low concentration is formed by ion implantation, a p+ type emitter diffusion layer 17 and an N+ type base diffusion layer 18 are formed by thermal diffusion or the like. Thereby a bipolar IC 10 having a vertical transistor is constitued in the manner in which the vertical transistor is formed.