The gain‐current coefficient and current density at transparency of GaAs/AlGaAs and InGaAs/GaAs/AlGaAs quantum‐well (QW) laser structures have been calculated as a function of the QW thickness by a straightforward numerical calculation. The optimum QW thicknesses are determined to be 100 and 105 A˚ for typical GaAs/AlGaAs and InGaAs/GaAs/AlGaAs QW laser structures, respectively, using the widely accepted semilogarithmic expression for threshold current density of QW lasers. These calculated optimum QW thicknesses agree with the reported experimental data very well. The reduction of the laser threshold current density as a result of using the optimum QW thickness is estimated to be 15% typically.