a semiconductor device includes a memory module board mounting thereon a plurality of dram devices , and a mount board mounting thereon the memory module board via a combination of socket and plug . the socket formed on the mount board has a pair of heat radiation guide plates attached onto the side surfaces of the socket . the heat radiation plates have a thermal conductivity of 1 watt / meter · k . the surface of the mount board onto which the socket is attached is a conductive sheet having a thermal conductivity of 1 watt / meter · k .