The method of frequency‐resolved optical gating (FROG) was applied to study the electric field reflected from MBE grown GaAs/AlGaAs quantum well samples after excitation with femtosecond laser pulses in resonance with the exciton transitions. The fluence of the incident laser pulses was varied by more than three orders of magnitude. In the linear regime we find good agreement of the FROG signals with the results of a dielectric model that takes into account the detailed structure of the sample. In the high intensity regime a strong enhancement of the reflected field due to the quantum well exciton transitions is observed.