Surface damage in GaAs has been studied by measuring the room‐temperature reflectance in the 3‐eV spectral region. Controlled levels of damage were created by implanting samples with known doses of 75‐keV argon ions. The damage from doses as low as 1011ions/cm2has been observed by studying the energy derivative of the reflectance (dR/dE)/R. As the damage level is increased, the optical reflectance structure broadens and hence the amplitude of (dR/dE)/Rdecreases. The sensitivity of this technique is comparable to or greater than that obtainable with other damage measurement techniques. The results for three other techniques (ellipsometry, channeling, and photoluminescence) are briefly discussed. Possible applications of the reflectance method are considered.