Post-growth annealing treatments in the range 400–600 °C are performed on GaSb/GaAs Interfacial Misfit grown samples. Current density–voltage (J–V), Capacitance–voltage (C–V), capacitance–frequency (C–F) and Deep Level Transient Spectroscopy (DLTS) measurements are performed on as-grown and annealed samples. Our studies show that possible defect compensation is observed with the annealing treatments, resulting in a significant improvement in the performances of the devices.