PURPOSE: To prevent an output from being affected by the voltage fluctuation of a voltage source due to noise and the like, by forming an impurity layer under a load gate operating layer, and forming, under the load gate impurity layer, a potential well which does not fluctuate by the effect of external noise and the like.

CONSTITUTION: A source voltage is applied between a first impurity layer 2 and a second impurity layer 4, and a specified voltage is applied to a semiconductor substrate 1. A constant voltage such as earth, which does not change by the effect of external noise and the like, is applied to a load gate 7. By applying the above unchangeable constant voltage, a potential well is formed under a load gate 7. This potential well is shallower than the voltage of the first impurity layer 2, and does not change by the effect of noise and the like. Independently of the ON-OFF state of an input gate, the value of the potential well is constant. Thereby, from the second impurity layer 3, an output is obtained which is not affected by noise independetly of the ON-OFF state of the input gate.