Wide-band-gap semiconductor materials such as gallium nitride (GaN) have superior material properties compared to silicon for use in devices like power electronics, laser diodes, and light-emitting diodes (LEDs). Where devices based on GaN-on-silicon substrates grow, bulk GaN substrates offer the potential to improve device performance, albeit at higher cost. We evaluated the manufacturing costs of bulk GaN substrates and the added cost of GaN epitaxy, and compared the result to the alternative GaN-on-silicon approach. GaN-on-silicon will remain the low-cost solution for wafers, but GaN-on-GaN can become competitive at the device level under the right conditions. As a result, bulk GaN wins in laser diodes, but it must race to become relevant in LEDs and power electronics by boosting yield and performance enough to make devices cost competitive.