In order to manufacture a thin and small semiconductor device at low cost, the semiconductor device and its manufacturing method are disclosed. The semiconductor device comprises: a film wiring substrate made of insulating resin; a semiconductor chip fixed to the main surface of the wiring substrate; conductive wires to connect terminals of the semiconductor chip and wirings on the main surface of the wiring substrate; an encapsulation made of insulating resin integrally laminated on the main surface of the wiring substrate and covering the semiconductor chip and the bonding wires; and conductors penetrating through the wiring substrate and having one ends connected to the wirings on the main surface of the wiring substrate and the other ends protruding to the rear surface of the wiring substrate to form external terminals formed of bump electrodes, wherein the external terminals form the ball grid array. The thickness of the semiconductor chip (100 .mu.m or smaller) is larger than that of the wiring substrate (70 .mu.m or smaller), and the thickness of the wiring substrate is larger than the external terminal (30 .mu.m or smaller). The thickness of the semiconductor device is 0.5 mm or smaller.