The crystallinity of a SrS:CeCl3 active layer for a thin-film electroluminescent (EL) device is strongly affected by the underlayer. Bright blue emission is achieved in a thin-film EL device having a strongly cub.(111)-oriented ZnS film as its underlayer. The maximum brightness of the device is 1100 nt under 5 kHz sinusoidal voltage excitation. The EL characteristics are discussed in relation to the X-ray diffraction pattern and photoluminescence spectra of the active layer.