To provide a board and a semiconductor device that reduces thermal expansion coefficient difference between the board and semiconductor element, and that between the board and the mounting board, to prevent the semiconductor element and mounting board from being damaged and enable precious board manufacturing, in terms of boards and semiconductor devices which electrically connect semiconductor elements and mounting boards having different basic thermal expansion coefficients.

A board comprises a metal base material 42 and a resin 38; a through hole 37 is formed on a metal base material 42 corresponding to a connection area A to which a semiconductor element 31 is connected; a through hole 36 with a diameter larger than that of the through hole 37 is formed on the metal base material 42, corresponding to a connection area B to which a mount board 41 is connected; then a resin 38 is applied to both through holes 36 and 37.

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