A method for fabricating a base for a semiconductor package is provided. The method operates by providing a carrier with conductive seed layers on the top surface and the bottom surface of the carrier, forming radio-frequency (RF) devices respectively on the conductive seed layers, laminating a first base material layer and a second base material layer respectively on the conductive seed layers, covering the RF devices, and separating the first base material layer the second base material layer, which contain the RF devices thereon, from the carrier to form a first base and a second base.