Ordered structure in GaInP alloys grown on (001) GaAs substrates by low‐pressure metalorganic vapor phase epitaxy has been investigated by means of x‐ray diffraction and transmission electron microscopy. We found a broad peak of CuPt I type (111)Bordering in the x‐ray measurements. X‐ray results gave the total amount of ordered region and the average size of each ordered domain. Room‐temperature photoluminescence peak energy anomalies were found to be related to the amount of the order phase.