Gallium NitrideGaN is known for its wide-energy bandgap of 3.4 eV and its high-efficiency as a semiconductor, which makes it a prime material for high-power, high-frequency, and low-noise systems. Specifically, GaN high electron-mobility transistors HEMTshave seen an increase in popularity due to its two-dimensional electron gas 2DEG that allows for increased mobility of un-doped GaN. In this work, GaN HEMTs were irradiated with a fluence of 2x1016ncm2 while maintaining a 99 percent fast-to-thermal neutron ratio. There were three phases to this work, the first was the design and fabrication of a photoneutron converter. The second was the design and implementation of a device testing suite in order to characterize the GaN HEMTs before, during, and after the experiment. The last was the analysis of the data showing the relationship of the electrical and physical characteristics of the devices with respect to the fast neutron fluence. The damage was also analyzed using a total displacement calculation for each layer of the device. The GaN HEMTs linearly degraded due to the high energy neutron displacements within the heterojunction layers.