The photoluminescence spectra were measured from 4 to 90 K for single-quantum-well structures of (Ga,In)As/(Al, In)As with well widths ${L}_{z}$=14.5 and 19.3 A\r{}. The optical transitions were observed from n=1 electrons in the conduction-band well to n=1 heavy holes (hh) and light holes (lh) in the valence-band well. Using the observed energy separation between hh and lh subbands, the well depth \ensuremath{\Delta}${E}_{v}$=120 meV for holes in the valence band and the corresponding well depth \ensuremath{\Delta}${E}_{c}$=740 meV for electrons in the conduction band were determined. This gives the relation of \ensuremath{\Delta}${E}_{c}$=0.85\ensuremath{\Delta}${E}_{g}$ which agrees with Dingle's rule for GaAs/(Al,Ga)As system.