Non-linear and stimulated emission of ZnSxSe1 − x/ZnSe multilayer structures grown by MOVPE on GaAs is investigated by means of high-density excitation spectroscopy using a high-resolution pulsed excimer-dye laser system as well as a picosecond titanium–sapphire laser for time-resolved measurements. Heterostructures with ZnSe layers or single and multiple quantum wells were grown in which the ZnSe layer widths were varied between 1 nm (strong quantum confinement) and 500 nm (quasi-bulk situation). The sulphur concentration in the ZnSxSe1 − x buffer, barrier and cap layers was chosen between x = 0.045 and x = 0.74 in order to find the most promising compromise with regard to maximum band offset to ZnSe for most efficient carrier confinement and suitable waveguiding properties depending on variation in the refractive index, and to highest structural quality of the actively emitting ZnSe layers. Stimulated emission is found to occur in all samples, being brightest in the sample with the lowest sulphur concentration in the cap and barrier layers. Its dynamical properties point to a probable interpretation in terms of electron–hole plasma creation, which, however, may not be the basic process in narrow-quantum wells or strongly structurally disturbed samples.