We demonstrate a novel GaN-based heterojunction field effect transistor (HFET) active-matrix circuit for an lightemitting diode (LED) microdisplay. Simulation results are shown with basic and improved circuits. Variations of process and material growth conditions are discussed by correlating device parameters with LED flow currents in this circuit. It shows that the HFET-LED control circuit approach provides a stability path to mitigate variations of LED currents during operations.