A semiconductor device includes a phase compensation circuit 6 using a MOS capacitor with a structure in which an insulating film is disposed between a gate electrode formed on a semiconductor substrate and a diffusion layer. The phase compensation circuit includes first and second MOS capacitors 14, 15. A gate electrode terminal of the first MOS capacitor is connected equivalently to a diffusion layer terminal of the second MOS capacitor that is a terminal opposite to the gate electrode terminal. A potential difference generating element 16 that generates a potential difference by allowing a current to flow therethrough is connected between a diffusion layer terminal of the first MOS capacitor and a gate electrode terminal of the second MOS capacitor. When the MOS capacitors having the voltage dependence are used, e.g., as a phase compensation circuit element of an operational amplifier, the MOS capacitance is not reduced, no matter the range of the input or output voltage of the operational amplifier, so that the phase margin will not reduced.