A semiconductor substrate has at least two active regions, each having at least one active device that includes a gate electrode layer, and a shallow trench isolation (STI) region between the active regions. A decoupling capacitor comprises first and second dummy conductive patterns formed in the same gate electrode layer over the STI region. The first and second dummy conductive regions are unconnected to any of the at least one active device. The first dummy conductive pattern is connected to a source of a first potential. The second dummy conductive pattern is connected to a source of a second potential. A dielectric material is provided between the first and second dummy conductive patterns.