Lattice matched ZnMgSe grown on InP is of considerable interest for its potential applications as a cladding layer due to the high band-gap energy (similar to 3.6 eV) and for use in intersubband devices such as quantum cascade lasers. Several lattice matched Zn0.5Cd0.5Se/Zn0.13Mg0.87Se quantum wells (QWs) were grown on InP (001) substrates. Emission ranging from the near UV to the visible spectral range was achieved by varying the thickness of the wells. The QW fundamental transition as function of the QW thickness was experimentally studied and modeled using an envelope calculation. The contactless electroreflectance measurements of a Zn0.5Cd0.5Se/Zn0.13Mg0.87Se single QW yielded multiple transitions from the QW, allowing us to estimate the conduction band offset of this heterostructure to be as high as 1.12 eV. (c) 2005 American Vacuum Society.