On studying the magnetoresistivity of GaAs‐GaInP heterostructures grown by low‐pressure metalorganic chemical vapor deposition in magnetic fields up to 12 T and at liquid‐helium temperatures, we have observed extremely high electron mobilities. Using the persistent photoconductivity effect, by illumination with red light, we reached a mobility of 780 000 cm2/(V s) at an electron density of 4.1×1011cm−2. This high electron mobility is confirmed by cyclotron resonance measurements.