To provide a semiconductor device capable of moderating thermal stress while suppressing a decrease in thermal conductivity of heat generated by a semiconductor element.

A semiconductor module comprises a circuit board, a semiconductor element bonded onto the circuit board by soldering, and fin units 13 bonded to the circuit board. The circuit board is composed by bonding a front metal plate to a surface of a ceramic substrate 14 and a rear metal plate 16 to a rear surface of the ceramic substrate. The fin units 13 which form an uneven shape in a side view are bonded to the rear metal plate 16. In the rear metal plate 16, an inter-fin groove 23 which moderates thermal stress caused by heat generated by the semiconductor element is formed between the fin units 13.