PURPOSE: To increase the junction capacitance of the collector-base with a small element area and to attain high integration, high reliability and high speed, by forming the base-collector junction vertically along a trench reaching the buried layer from the base region.

CONSTITUTION: After an N-type buried layer 11, an N-type epitaxial layer 13 and an element-separating oxide film 12 are formed on a P-type semiconductor substrate 10, a silicon oxide film 12A and a silicon nitride film 22 are formed on the region for the element to be formed, and a trench 24 reaching the epitaxial layer 13 is formed using photo resist 23 as a mask. After removing the photo resist 23, a P-type diffusion layer 14 is formed in the trench 24 and the trench 24 is etched using the nitride film 22 as a mask till it reaches the buried layer 11. An N-type diffusion layer 15 shallower than the P-type diffusion layer 14 is formed inside the trench and the trench is filled with polycrystalline silicon 18 having N-type impurities doped. Next, P-type impurities are ion- implanted to form a base region 16, and an N-type emitter region 17 is formed.