The growth of ZnS and ZnCdS alloy layers on GaP substrates have been carried out using molecular beam epitaxy with ZnS and S sources. A Zn flux is used to protect the substrate surface during the surface oxide removal and growth can be started with a 2 x 4 reconstruction in analogy with the growth of high-quality ZnSe. Lattice-matched ZnCdS layers show only intense excitonic spectra and an X-ray FWHM of 40 arcsec has been observed.