A first semiconductor layer consisting of AlGaInP is formed on a substrate consisting of GaAs by crystal growth while adding magnesium (Mg) that is a p-type dopant to the first semiconductor layer. A second semiconductor layer consisting of GaAs is then grown on the first semiconductor layer without adding any magnesium to the second semiconductor layer. Thus, the second semiconductor layer can prevent unintended doping (memory effect) produced by magnesium.