A compact semiconductor device with an isolator. The semiconductor device includes two chips, namely a first semiconductor chip and a second semiconductor chip which are stacked with the main surfaces of the semiconductor chips partially facing each other. A first coil and a second coil which are formed in the first semiconductor chip and the second semiconductor chip respectively are arranged to face each other so as to be magnetically coupled during operation of the semiconductor device. The pair of first and second coils make up an isolator. The first coil is arranged in a manner to overlap part of the circuit region of the first semiconductor chip in plan view and the second coil is arranged in a manner to overlap part of the circuit region of the second semiconductor chip in plan view.