A semiconductor package using a polymer substrate is disclosed and may include a polymer cavity structure comprising first metal traces, a micro-electro mechanical systems (MEMS) device and a semiconductor die bonded to a first surface within a cavity of the cavity structure, and a substrate coupled to the cavity structure and comprising second metal traces coupled to the first metal traces. The substrate may enclose the MEMS device and the semiconductor die. Ground traces may be on external surfaces of the polymer cavity structure. Ball lands may be on a surface of the substrate opposite to a surface with the second metal traces. The first metal traces may extend from the first surface of the polymer cavity structure up a sidewall of the cavity and to conductive patterns on a top surface of the polymer cavity structure.