PURPOSE: To form a high reliable groove capacitance by a method wherein a groove is formed by removing a part of working parts by etching using the anisotropic etching technique, after working a groove forming part and a semiconductor base plate surface at its periphery, into the circular shape convexed downward.

CONSTITUTION: A silicon dioxide film 32, a silicon nitride film 33 and a silicon dioxide film 34 are formed in order on a single crystal silicon base plate 31, then its surface is covered by a photoresist 35 removing a capacitance forming region. Next, the films 34, 33, 32 are removed by etching in order by the anisotropie etching technique. A silicon dioxide film 36 is formed, a silicon base plate 31 on the capacitance forming region being oxided. Subsequently, when the film 36 is removed by the anisotropic etching technique, the surface of the silicon base plate becomes to the shape which is applied the shape of the film 36y as it is, and differences in level convexed downward slowly are formed at the center and the end part of the opening part. Furthermore, the groove and films are etched, and an insulation film 37 and an electrical conductivity material 38 are formed.