This heat sink has bonded on one surface a member to be bonded, and has a cooling member in contact with the other surface. The heat sink is provided with a metal plate having a thermal expansion coefficient larger than that of the member to be bonded, and the metal plate is provided with a center portion where the member to be bonded is bonded, and a plurality of linear peripheral slits formed in a whirl-like radial manner such that the linear peripheral slits surround the center portion.