For this study, a microcomputer‐controlled electrolyte electroreflec‐tance (EER) system has been set up. EER measurements are carried out on samples of Ga1‐xAlx, As alloys in the photon energy range of 1.4 to 4.2 eV at room temperature. TheE0, E0+?0, E1andE1+?1transitions have been determined as a function of alloy compositionx.The transition energies at critical points show quadratic dependence on the alloy composition, with the relationE(x)=a+bx+cx2.Based on this relation, the EER technique has been utilized to study the variations in composition across the surface of the sample. This technique is nondestructive and can readily be employed under atmospheric conditions at room temperature. This method is sensitive enough to determine the changes of composition?xwithin a range of\%with a spatial resolution of 150μm.