Abstract The electrostatic potentials and electronic structure of an AlAs/GaAs double quantum well (DQW) heterostructure are determined through ab initio computations. The study of the potentials along the growth direction establishes a clear relation between the microscopic structure and the relevant macroscopic properties of the heterostructure, namely, the DQW dimensions and the band offsets. At nanometric scale, the one electron effective potential energy is a DQW and the valence band edge electronic states are confined along the growth direction. Such states coincide qualitatively with those analytically obtained through the so‐called envelope function/effective mass approximation.