A method of forming a semiconductor package structure includes providing a first wafer-level package structure having a die region surrounded by a scribe line region. The first wafer-level package structure includes a first encapsulating layer, a first redistribution layer (RDL) structure formed on the first encapsulating layer, a first antenna element formed in the first RDL structure and corresponding to the die region, and a semiconductor die in the first encapsulating layer and corresponding to the die region. A second wafer-level package structure is bonded onto the first RDL structure using a first adhesive layer. The second wafer-level package structure includes a second encapsulating layer attached to the first adhesive layer, and a second antenna element formed on the second encapsulating layer. The second antenna element and the first antenna element form a pitch antenna after the bonding of the second wafer-level package structure.