In this work we employed photoreflectance spectroscopy over the temperature range 11-300 K to investigate the heterointerfaces of a strained piezoelectric InGaAs/GaAs single quantum well structure grown on a (111)A GaAs substrate by metalorganic vapor phase epitaxy. Photoreflectance spectroscopy measurements in combination with a theoretical analysis using the quantum well structural parameters obtained by high-resolution x-ray diffractometry enabled us to evaluate separately the abruptness and roughness of the quantum well interfaces. The excellent agreement between the experimental and calculated transition energies for a quantum well structure with a well width of 41 Å and 13% In demonstrates that the heterointerfaces are abrupt. From a theoretical analysis of the temperature dependence of the photoreflectance broadening parameters, based on the Bose-Einstein phonon-coupling model, we determined the longitudinal optical phonon energy and the electron-phonon coupling strength. This analysis shows an interface roughness of less than ±1 monolayer. These results in conjunction with the observation of a narrow photoluminescence linewidth of 9.1 meV indicate the achievement of essentially atomically smooth interfaces in a highly strained (∼1%) piezoelectric InGaAs/GaAs quantum well structure.