GaInP/AlInP quasi‐quaternary (QQ) compounds grown by gas‐source molecular‐beam epitaxy were systematically investigated. Quasi‐quaternary properties were obtained with GaInP/AlInP short‐period superlattices when the thickness of the AlInP layers was less than 3 ML. Equivalent band‐gap values of QQ compounds were defined in terms of the layer thickness ratios of the GaInP and AlInP layers. Using GaInP/AlInP quasi‐quaternary compounds, 607–640‐nm wavelength QQ lasers with 20‐nm QQ active layers were fabricated. Threshold current densities as low as 1.5 kA/cm2were attained for QQ lasers emitting at 635 nm without the presence of strain or quantum‐well effects.