We report the observation of strong photoinduced intersubband absorption in a lattice‐matched In0.53Ga0.47As/InP multiquantum well structure. The absorption, which is induced by optical pumping with an above gap light is polarized along the growth direction and is assigned to the transition from the first to the second subband in the conduction‐band quantum well. The measured intersubband transition energy is in very good agreement with an effective‐mass‐approximation model including nonparabolicity effects. Assuming a linear dependence of the electron effective mass on the energy, we find a nonparabolicity parameter of 1.35±0.25 eV−1for the In0.53Ga0.47As well.