Doping dependence of intersubband absorption in In0.53Ga0.47As/In0.52Al0.48As multiquantum wells (MQWs) grown by molecular beam epitaxy is investigated. The MQWs having a constant well width of 130 A˚ are uniformly doped to a sheet carrier concentration of 4×1011–1×1013cm−2. AboveNs=1.8×1012cm−2, the intersubband absorption from the second to the third subband is observed, as well as from the first to the second, which agrees well with theoretical calculations.