In aspects of the assembly jig and method of the invention, when a packaging substrate is curved concaving upward at temperatures of melting solder, the gap between the assembly jig and the packaging substrate can be made smaller than the dimension of the sum of the thickness of the semiconductor chip and the thickness of the melted solder by allowing a part of the bottom surface of the chip positioning piece to become always, or substantially always, in contact with the upper surface of the packaging substrate owing to the weight of the chip positioning jig itself. As a consequence, the semiconductor chip does not slip aside out of the opening of the chip positioning piece. Therefore, the semiconductor chip can be positioned accurately on the packaging substrate.