A monolithically integrated semiconductor assembly is presented. The semiconductor assembly includes a substrate including silicon (Si), and gallium nitride (GaN) semiconductor device is fabricated on the substrate. The semiconductor assembly further includes at least one transient voltage suppressor (TVS) structure fabricated in or on the substrate, wherein the TVS structure is in electrical contact with the GaN semiconductor device. The TVS structure is configured to operate in a punch-through mode, an avalanche mode, or combinations thereof, when an applied voltage across the GaN semiconductor device is greater than a threshold voltage. Methods of making a monolithically integrated semiconductor assembly are also presented.