The microstructural, optical, and electronic characteristics of both Cl-doped ZnMgSSe epilayers and Schottky diodes grown by the molecular beam epitaxy method on n(+)-type GaAs (100) substrates with different thicknesses of Cl-doped ZnSe buffer layers were investigated via three measurements: transmission electron microscopy, photoluminescence, and deep level transient spectroscopy. The V-shaped stacking faults, originating ht or near the ZnSe:Cl (buffer layer)/GaAs interface and extending into the ZnMgSSe:Cl epilayer, were discovered to have the evident inclination to exist in samples with thicker ZnSe:Cl buffer layers and higher growth-temperatures. Evidence also revealed that the stacking faults not only produced poor optical quality of ZnMgSSe:Cl thin film, but also created more interface state densities at the Au/n-type ZnMgSSe:Cl Schottky junction. Such results are the main factors to damage the I-V characteristics of Au/n-type ZnMgSSe:Cl Schottky diode, including the less forward conduction current density, the bigger turn-on voltage, and the larger reverse leakage current followed by the smaller reverse breakdown voltage.