Femtosecond intraband relaxation dynamics of hot carriers in highly excited states of GaAs, AlGaAs, and AlGaAs/GaAs multiple quantum well (MQW) structures are studied at room temperature using the equal‐pulse correlation technique. Initial carrier lifetimes of 35, 60, and 50 fs are measured for GaAs, Al0.32Ga0.68As, and MQW structures for excitation with 2.02‐eV photons at low carrier densities, and are in reasonable agreement with calculated scattering rates. The carrier‐density dependence of these lifetimes is measured for densities in the range 1.5×1017–5×1019cm−3.