A semiconductor laser device includes a resonant cavity formed on a GaAs substrate, the resonant cavity including a quantum well (QW) active layer structure having a GaInNAs(Sb) well layer and a pair of barrier layers. The QW structure has a conduction band offset energy (.DELTA.Ec) equal to or higher than 350 milli-electron-volts (meV) between the well layer and the barrier layers, and each of the barrier layers a tensile strain equal to or lower than 2.5%.