In$-{x}$Ga1- $-{x}$N solar cells are ideal for use in extreme temperature applications due to their wide band gap and chemical stability. In this paper, the details are given for the growth, fabrication, and characterization of In $-{x}$Ga1- $-{x}$N multiple quantum well solar cells designed for high temperatures. Materials characterization confirms basic optical and physical properties of the layers. External quantum efficiency, dark current-voltage, 1-sun current-voltage, and 300-sun high intensity pulsed solar simulator current-voltage measurements were taken at varied temperatures. Correlations are made between different characterization methods to draw conclusions about device behavior. Photovoltaic performance for $V-{{\rm{OC}}}$, $W-{{\rm{OC}}}$, $J-{{\rm{SC}}}$, and fill factor is given at multiple temperatures from 25 °C to 600 °C.