A semiconductor device in which a plurality of semiconductor elements are bonded onto at least one electrode pattern on an insulator substrate formed a plurality of electrode patterns on the main surface, each of the electrodes of the semiconductor element being electrically connected to the electrode pattern, the other surface of the insulator substrate being bonded to a heat dissipating base, the upper surface of the heat dissipating base being covered with a member for cutting off the semiconductor elements from the outer environment, terminals electrically connecting the electrodes on said insulator substrate and the electrode placed outside the cutoff member being provided, wherein the material of the heat dissipating base has a linear expanding coefficient larger than the linear expansion coefficient of the semiconductor element and smaller than three times of the linear expansion coefficient of the semiconductor element, and a thermal conductivity larger than 100 W/mK, the semiconductor elements being arranged on at least one electrode surface and in at least two regions divided by the other electrode surface on the insulator substrate.