The room temperature reflectance spectra of the ternary compounds of CdSnAs2, CdGeAs2, ZnSnAs2, ZnGeAs2, and ZnSiAs2 have been determined in the energy range 1.5–6.0 eV by reflectance, electroreflectance, and thermoreflectance techniques. Similar measurements have been made on alloys of the systems In2(1−x)ZnxSnxAs2 and In2(1−x)CdxSnxAs2. These latter data have enabled the spectral peaks of the ternary compounds to be labelled and distinction made between the zincblende peaks and extra peaks due to the chalcopyrite structure. Possible band transitions producing the extra peaks are discussed.