WIRING BOARD

PROBLEM TO BE SOLVED: To improve adhesion between the insulation substrate and heat radiating layer of a wiring board, after the substrate and layer have been simultaneously baked and to make the thermal strain of the insulation substrate very small. SOLUTION: The wiring board is provided with the insulation substrate 1, which is made of a ceramic containing Al2 O3 as the main component and Mn in an amount of 2-10 wt.% in terms of Mn2 O3 and having a relative density of >=95%, and has a mounting section 1A for mounting a semiconductor element 3 on its upper surface; the wiring board also provided with a plurality of through-conductors 2 which are made of a conductor material containing Cu in an amount of 10-70 vol.% and W and/or Mo in an amount of 30-90 vol.% and formed the mounting section 1A and its periphery to the lower surface of the substrate 1, and an electrode section 1B formed on the upper surface of the substrate 1. On the surface of the substrate 1, excluding the electrode section 1B, the heat-radiating layer 4 made of a conductor material and connected to the conductors 2 on the lower surface of the substrate 1 is formed, and the mean particle diameter of W and/or Mo in the layer 4 is adjusted to be 1-5 μm.