A semiconductor package has a semiconductor device chip and a flexible substrate having a thermoplastic insulating resin layer. An electrode provided on the flexible substrate is connected to a predetermined electrode of the semiconductor device chip and sealed by the thermoplastic insulating resin layer. The flexible substrate is bent and provided with electrodes on the electrode-bearing and other surfaces. The flexible substrate has multi-layered wirings. Grooves or thin layer portions having a different number of wiring layers are formed at bends of the flexible substrate or regions including the bends, thereby creating a cavity at a portion in which a semiconductor device is packaged. Then, the flexible substrate is bent at predetermined positions to form a semiconductor package which does not depend on the outer dimensions of the semiconductor device chip.