Wide bandgap GaN semiconductor has unique material properties that promise high power and high frequency electronics systems. Compared to conventional Si material, GaN has much larger bandgap and lower intrinsic carrier density, which will allow for efficient electronic devices working at high temperatures. Compared to other high temperature materials such as SiC, GaN has much higher mobility, which will lead to electronic device with much higher speed and microsystems with higher clock frequency. In this proposal, we plan to demonstrate a GaN-based microprocessor that can work efficiently under high temperature (e.g., > 500°C), which is the first of its kind. Fundamental studies will be performed on the high temperature properties of GaN devices including material defects, electron transports, and thermal stabilities, and their impacts on the performance and reliabilities of GaN microprocessors will be discussed. An interdisciplinary approach is proposed which includes material growth and characterization, TCAD-based device/process simulations, microprocessor chip fabrication, and comprehensive high temperature characterizations. The realization of this microprocessor represents a potentially disruptive technology that will enable electronics system based on wide bandgap GaN devices with greater efficiency, much reduced size and weight, and higher operation temperature, all of which are highly desirable for various NASA and space applications.