PURPOSE: To prevent a deep groove from being cut in a shallow groove forming region and to hollow out a groove accurately controlling it in depth.
CONSTITUTION: A buried collector layer 2, an N-type epitaxial layer 3, a silicon oxide film 4, a silicon nitride film 5, a polycrystalline silicon film 6, and a silicon oxide film 7 are formed on a P-type silicon substrate 1 [figure (a)]. The film 7 on a collector isolating region 3a is removed, and then the films 4 to 7 on an element isolating region 9a are removed [figure (b)]. A part of a silicon substrate where the element, isolating region 9a is located is hollowed as deep as prescribed. At this point, the polycrystalline silicon film 6 on the collector isolating region 8a is removed at the same time [figure (c)]. Thereafter, the films 4 and 5 on the collector isolating region 8a are removed, and the silicon substrate 18 hollowed out as deep as prescribed.