The conduction-band offset ΔEc has been determined for molecular beam epitaxy (MBE) grown GaAs/In0.2Ga0.8As single quantum well structure,by measuring the capacitance-voltage profiling, while taking into account a correction for the interface charge density, and the capacitance transient resulting from thermal emission of carrier from the quantum well, respectively.We found that ΔEc=0.227eV,corresponding to about 89% ΔEg,from the C-V profiling; and ΔEc=0.229eV, corresponding to about 89.9% ΔEg, from the deep level transient spectroscopy (DLTS) technique. The results suggest that the conduction-band discontinuity ΔEc obtained from the C-V profiling is in good agreement with that obtained from the DLTS technique.