The relaxation of the electron temperature in CdSxSe1−xwas measured by transmission and transient grating experiments using fs light pulses. As compared with ordinary ambipolar diffusion, at high excitation a pronounced delayed rise and a faster decrease of the diffraction signal was observed. A theoretical model that includes one‐ and two‐photon excitation, gap shrinkage, diffusion, and temperature relaxation explains these experimental findings as a result of temperature relaxation with a characteristic time constant of 1±0.2 ps.