In an embodiment, a semiconductor structure includes a multi-chip package system (MCPS). The MCPS includes one or more dies, a molding compound extending along sidewalls of the one or more dies, and a redistribution layer (RDL) over the one or more dies and the molding compound. The semiconductor structure also includes at least one sensor coupled to the RDL, with the RDL interposed between the at least one sensor and the one or more dies. The semiconductor structure further includes a substrate having conductive features on a first side of the substrate. The conductive features are coupled to the RDL. The substrate has a cavity extending from the first side of the substrate to a second side of the substrate opposite the first side, and the at least one sensor is disposed in the cavity.