GaN-on-Si epitaxial wafers vie with GaN-on-sapphire for LED supremacy even as GaN-on-sapphire is the material of choice for 90% of LEDs manufactured today. Even though silicon is cheap and abundant and the mature microelectronics industry has made high-quality eight-inch and 12-inch silicon substrates and compatible facilities readily available, there are challenges to commercializing GaN-on-Si wafers at scale. Wafer diameter and cost are critical metrics for LED performance and overall system costs. While moving to larger diameter wafers will improve die output, it reduces wafer yield. With lowering substrate costs,improving wafer yields, availability of larger substrates and increasing die throughput GaN-on-sapphire wins. As a result, GaN-on-Si with unproven performance and reliability must race to stay relevant as the window of opportunity closes.