AbstractPhotoreflectance (PR) and contactless electroreflectance (CER) spectroscopies have been used to study optical transitions in an InP‐based laser structure emitted at 1.55 μm with the active region including InAs quantum dashes (QDashes). Optical transitions related to all relevant parts of the structure, i.e. In0.53Ga0.05Al0.42As n‐ and p‐type cladding layers, quaternary In0.53Ga0.23Al0.24As QDash barrier layers, InGaAlAs‐GRINSCH region, and InAs QDashes have been clearly observed at room temperature. Moreover, it has been found that some of the transitions are not observable in CER spectra whereas they are very strong in PR spectra. This phenomenon is associated with different modulation mechanisms in the two electromodulation techniques. It means that the combination of PR and CER techniques with traditional photoluminescence measurements allows much better characterization of the electronic structure for semiconductor devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)