The room temperature pulsed operation of In0.49Ga0.31Al0.20P/In0.49Ga0.51-x AlxP/In0.49Ga0.31Al0.20P(x=0.00–0.03) double heterostructure (DH) laser diodes have been achieved for the first time. The lasing wavelength was 0.66–0.68 μm with a threshold current density of 2.6–3.6×104A/cm2 at 26 °C. These results were achieved by growing DH wafers by molecular beam epitaxy (MBE). Key points in the successful MBE growth of these DH wafers were, first, the realization of low resistance p‐type and n‐type InGaAlP layers by reducing contamination in the growth chamber. This was done by installing a substrate loading room with an interlock valve and a substrate transfer mechanism. The second was the realization of an abrupt p‐n junction by the use of Si instead of Sn as an n‐type dopant.