We report the first observation of normal incidence infrared absorption due to interconduction subband transitions in AlAs/AlGaAs x‐valley multiquantum wells. Infrared absorption measurements were performed on samples grown on , , , and  substrates with normal incidence radiation at wavelengths of 5–20 μm. Two absorption peaks were observed in the  and  multiquantum wells with well widths of 40 Å and sheet doping concentrations of 1012 cm−2. One peak, due to transitions between the ground state and the continuum band occurred at 7.1 μm; a second peak originating from interconduction subband transitions between the ground state and the first excited state occurred at 17 μm. The experimental results indicate the potential of these novel structures for use as normal incidence infrared photodetectors.