The present invention provides a mount structure that withstands large thermal stress caused by a large joint area and suppresses occurrence and development of cracks caused by repeated temperature changes. The mount structure includes two members that are bonded to each other with a bonding material layer having a first interface layer and a second interface layer at the interfaces with the two members. The bonding material layer contains a first intermetallic compound and a stress relaxation material. The first intermetallic compound has a spherical, a columnar, or an oval spherical shape, and the same crystalline structure as the first interface layer and the second interface layer, and partly closes the space between the first interface layer and the second interface layer. The stressrelaxation material contains tin as a main component, and fills around the first intermetallic compound.