We propose a method to determine the band offset of a heterojunction based on the elimination of the diffusion potential. In0.5Ga0.5P/GaAs heterojunction samples were used for demonstration of this method. As many error sources related to the determination of diffusion potential are avoided in our case, the more accurate value of 137±5 meV has been obtained for the conduction‐band discontinuity. ©1996 American Institute of Physics.