A semiconductor assembly includes a multilayer wiring board including at least three insulating layers, first, second and third insulating layers and a semiconductor device attached to one principal surface of the first insulating layer. The first, second and third insulating layers are stacked in this order. The multilayer wiring board further includes a heat-insulating member made of a material having a lower thermal conductivity than the insulating layers. The heat-insulating member is disposed between the first and second insulating layers or next to the first insulating layer at a side opposite to the one principal surface.