Despite great progress in perovskite/silicon tandem solar cells’ device performance, their susceptibility to potential-induced degradation (PID) remains unexplored. In this study, we find that applying a voltage bias of −1,000 V to single-device perovskite/silicon tandem modules at 60°C for ∼1 day can cause a ∼50% loss in their power conversion efficiency, which raises concerns for tandem commercialization. We found no accumulation of Na+ in the perovskite or silicon photon absorbers. Consequently, no obvious shunt is observed in our silicon subcells. We also find that elements diffuse from the perovskite into the module encapsulant during PID testing. We argue that this diffusion is the main PID mechanism in our tandem modules. While applying a large positive voltage bias can partially recover this PID, introducing barriers or structures to prevent elemental diffusion out of the perovskite may be required to mitigate this degradation phenomenon.