Disclosed are a semiconductor device wherein warping of a semiconductor chip due to a sudden temperature change can be prevented without increasing the thickness, and a semiconductor device assembly. The semiconductor device comprises a semiconductor chip, a front side resin layer formed on the front surface of the semiconductor chip by using a first resin material, and a back side resin layer formed on the back surface of the semiconductor chip by using a second resin material having a higher thermal expansion coefficient than the first resin material. The back side resin layer is formed thinner than the front side resin layer.