[en] The electrical and optical properties of the lattice-mismatched InGaAs/GaAs heterostructures, with partial strain relaxation, were studied by deep level transient spectroscopy (DLTS) and photoreflectance (PR) spectroscopy, respectively. In the samples one of deep electron traps, revealed by DLTS, was ascribed to misfit dislocations at the interface, for which capture kinetics, concentration depth profiles and the type of electronic states have been specified. Room temperature PR spectroscopy was used for analysing the effect of residual strain on the optical response from the samples, i.e. interband transitions and the valence band splitting