PURPOSE: To enable a capacitor to be less affected by noises produced inside a board and set stable in performance by a method wherein a well is formed, and the capacitor is grounded through the intermediary of a grounding electrode connected to the well concerned.

CONSTITUTION: A semiconductor device is equipped with a first conductivity-type semiconductor substrate 10, a field oxide film 11, and a capacitor oxide film 13 formed on the field oxide film 11, wherein impurities are introduced under the field oxide film 11 to form a second conductivity type well 17. Furthermore, a grounding electrode 18 is provided so as to ground the well 17. By this setup, even if the substrate 10 fluctuates in potential due to the noises or the like of an external power supply, the lower electrode 12 of the capacitor 13 formed through the intermediary of the field oxide film 11 is less affected by a change in substrate potential, so that the capacitor 13 is enhanced in capacity stability.