We discuss the optical properties in thin quantum boxes based on a theoretical analysis that rigorously treats excitonic confinement effects in the intermediate regime between zero and two dimensions. Our theory can exactly analyze not only the excitonic ground state but also higher energy states, and thus can simulate whole absorption spectra near the band edge region. We also report novel exciton electro‐absorption effects found in the intermediate confinement regime. ©1996 American Institute of Physics.