PURPOSE: To protect a semiconductor device against the effect of potential fluctuation by a method wherein a dedicated voltage wire is provided for a well separately from a voltage wire used for supplying a prescribed voltage to a transistor.
CONSTITUTION: An N-type well region 22 is formed on the surface of a P-type silicon substrate 21 (or a P-type well region). For instance, a part of the flip- flops in a serial access memory is formed in the N-type well region 22. An N + -type diffusion region 23 is formed on the surface of the N-type well region 22. The N + -type diffusion region 23 serves as a region which comes into contact with a power wire 24 to supply an electric power to the well region 22, and the power wire 24 dedicated to a well is connected to the N + -type diffusion region 23. One or more of the N + -type diffusion region 23 are provided to the surface of the well region 22 depending on the size of a well. The well-dedicated power wire 24 is not used for supplying another power voltage Vcc. A normal power wire 25 is also provided in parallel with it separately from the well- dedicated power wire 24.