To improve the joining strength between semiconductor chips. In a semiconductor device, a first semiconductor chip includes a first joining surface including a first insulating layer, a plurality of first pads to which a first inner layer circuit insulated by the first insulating layer is electrically connected, and a linear first metal layer arranged on an outside of the plurality of first pads. A second semiconductor chip includes a second joining surface joined to the first joining surface, the second joining surface including a second insulating layer, a plurality of second pads that are arranged in positions facing the first pads and to which a second inner layer circuit insulated by the second insulating layer is electrically connected, and a linear second metal layer arranged in a position facing the first metal layer. A width of the first metal layer and the second metal layer is a width based on a joining strength between the first insulating layer and the second insulating layer and a joining strength between the first metal layer and the second metal layer in an area from an end portion of the first semiconductor chip to the first pad.