Provided are a method of forming an electromagnetic interference (EMI) shielding layer of a ball grid array (BGA) semiconductor package, and a base tape used in the method, and more particularly, a method of forming a shielding layer for blocking EMI, on an upper surface and lateral surfaces of a BGA semiconductor package having a lower surface, on which a plurality of solder balls are formed, and a base tape used in the method.According to the method of forming an EMI shielding layer of a BGA semiconductor package, the EMI shielding layer may be formed on the BGA semiconductor package quickly, easily, and effectively by using the base tape, thereby not only improving process productivity but also remarkably reducing the manufacturing costs.