Semiconductor dies including ultra-thin wafer backmetal systems, microelectronic devices containing such semiconductor dies, and associated fabrication methods are disclosed. In one embodiment, a method for processing a device wafer includes obtaining a device wafer having a wafer frontside and a wafer backside opposite the wafer frontside. A wafer-level gold-based ohmic bond layer, which has a first average grain size and which is predominately composed of gold, by weight, is sputter deposited onto the wafer backside. An electroplating process is utilized to deposit a wafer-level silicon ingress-resistant plated layer over the wafer-level Au-based ohmic bond layer, while imparting the plated layer with a second average grain size exceeding the first average grain size. The device wafer is singulated to separate the device wafer into a plurality of semiconductor die each having a die frontside, an Au-based ohmic bond layer, and a silicon ingress-resistant plated layer.