Vacuum ultraviolet reflectivity measurements of three thin‐film electroluminescent phosphors, zinc sulfide (ZnS), strontium sulfide (SrS), and strontium‐calcium thiogallate (Sr₀.₄₅Ca₀.₅₅Ga₂S₄), are reported using thin‐film samples. Measured ZnS reflectivity peak positions are in agreement with values previously reported in the literature. SrS room temperature reflectivity measurements are found to be consistent with previously reported low temperature measurements. Reflectivity measurements of Sr₀.₄₅Ca₀.₅₅Ga₂S₄ are reported for the first time; the reflectivity spectrum is found to rise monotonically above the band gap and to exhibit almost no structure, except for a small shoulder at ∼6.8 eV and a single, broad peak at ∼8.5 eV. The unusual nature of the Sr₀.₄₅Ca₀.₅₅Ga₂S₄ reflectivity spectrum is attributed to positional disorder in the stoichiometric thiogallate film.