The optical perturbation of an infrared wave guided in a GaAs epitaxial layer allows us to measure the two‐photon absorption coefficient &bgr; for the wavelength &lgr;=1.06 &mgr;m. The use of optical properties of free carriers induced by the two‐photon effect and of guided optical wave techniques strongly enhances method accuracy. The result (&bgr;=0.06 cm MW−1) is in good agreement with the most recent bulk measurements and the theoretical values.