The invention provides a semiconductor device capable of suppressing a short channel effect and fluctuation in a threshold. The semiconductor device includes: a plurality of first transistors formed in a first region in a semiconductor layer in a multilayer substrate having, on a semiconductor substrate, an insulating layer and the semiconductor layer in order from the semiconductor substrate; a plurality of second transistors formed in a second region in the semiconductor layer; a first impurity layer formed in a region opposed to the first region in the semiconductor substrate; a second impurity layer formed in a region opposed to the second region in the semiconductor substrate; and a first isolation part that isolates the first and second regions from each other and electrically isolates the first and second impurity layers from each other to a degree that at least current flowing between the first and second impurity layers is interrupted.