Highly strained InxGa1−xAs/GaAs quantum well structures on GaAs substrates were grown by molecular‐beam epitaxy. Even with high In composition (0.4 or higher), sharp spectra were obtained from samples grown at 400 °C due to the reduction of In surface segregation. The full width at half maximum of the photoluminescence spectrum from a 6.4‐nm‐thick (21 monolayers) In0.42Ga0.58As/GaAs single quantum well at 77 K and at room temperature was only 9.78 and 18.4 meV, respectively. The peak wavelength of this sample at room temperature was 1.223 &mgr;m. The theoretically calculated peak wavelengths, using a finite square‐well model are in good agreement with the experimental ones over a wide In composition range (between 0.14 and 0.44), and with well widths between 6 and 53 monolayers. This study suggests that the performance of pseudomorphic devices can be improved by using high‐quality InxGa1−xAs layers with high In composition pseudomorphically grown on GaAs substrates. ©1995 American Institute of Physics.