An
isolator is configured by a transmission circuit, a
transformer, and a reception circuit. A first coil of the
transformer is disposed on a back surface of a first
semiconductor substrate; a transmission circuit and a second coil of the
transformer are disposed on a front surface. The first coil is embedded within a coil trench, is led out through an embedded via-
metal-film to a substrate front surface, and is electrically connected to the transmission circuit. The second coil is disposed on an insulating layer of the substrate front surface. The reception circuit is disposed on a front surface of a second
semiconductor substrate. The second coil and the reception circuit are electrically connected to each other by connecting first and third
electrode pads disposed respectively on the front surfaces of the first and second
semiconductor substrates through wires.