A semiconductor module 10 includes a ceramic substrate having a front surface on which a semiconductor element 12 is mounted and a rear surface on the opposite side of the front surface, a front metal plate 15 joined to the front surface, a rear metal plate 16 joined to the rear surface, and a heat sink 13 joined to the rear metal plate 16. The rear metal plate 16 includes a joint surface 16b that faces the heat sink 13. The joint surface 16b includes a joint area and a non-joint area. The non-joint area includes recesses 18 which extend in the thickness direction of the rear metal plate 16. The joint area of the rear metal plate 16 is in a range from 65% to 85% of the total area of the joint surface 16b on the rear metal plate 16. As a result, excellent heat dissipating performance can be achieved while occurrence of distortion and cracking due to thermal stress is prevented.