A semiconductor device includes a semiconductor layer having a first surface, an insulating layer formed at the first surface of the semiconductor layer, a Cu conductive layer formed on the insulating layer, the Cu conductive layer made of a metal mainly containing Cu, a second insulating layer formed on the insulating layer, the second insulating layer covering the Cu conductive layer, a Cu pillar extending in a thickness direction in the second insulating layer, the Cu pillar made of a metal mainly containing Cu and electrically connected to the Cu conductive layer, and an intermediate layer formed between the Cu conductive layer and the Cu pillar, the intermediate layer made of a material having a linear expansion coefficient smaller than a linear expansion coefficient of the Cu conductive layer and smaller than a linear expansion coefficient of the Cu pillar.