An investigation of the finite depth square well model is presented in this article: model features and limitations, concerning size dependent band gap of semiconductor quantum structures, are presented and discussed. Model predictions are compared with large sets of experimental data for III–V, II–VI and lead salt semiconductor quantum dots and quantum wires. Matrix influence on the confinement is studied by modeling experimental results for colloidal CdS, CdSe, CdTe and InP quantum dots. The effect of quantum structure dimensionality is investigated and successfully simulated for colloidal CdSe and InP experimental data and Si first-principle calculations. Finally, model limitations for narrow band gap semiconductors are studied and discussed.