Abstract: Disclosed is a thin plate member for forming a semiconductor package, having a recess for receiving a semiconductor chip. The thin plate is composed of sintered metal, e.g. sintered copper or sintered alluminum alloy. A sintered metal body being porous and having a shape which is close to the shape of the thin plate member is prepared, and it is sized into the shape of the thin plate member. The sintered alluminum alloy comprises 0.4 to 0.8% by weight of magnesium, 0.2 to 0.6% by weight of silicon and the balance aluminum and has a structure comprising an aluminum phase being formed of aluminum particles and an alloy phase being composed of magnesium, silicon and aluminum and interposing between the aluminum particles, and the sintered copper has a metallographic structure comprising a phase of copper particles.