Results of ir and Raman investigations on trigonal layer-structured Si2Te3 single crystals are reported. The ir reflection spectrum with E⊥c exhibits seven reststrahl-like bands, whereas the corresponding spectrum with E∥c shows only one very small bump. Values for ε0 and ε∞ are given. The Raman spectra are very rich in structure and can only be interpreted qualitatively as being a mixture of single phonon lines and one- and two-phonon density-of-states contributions. One-phonon density-of-states effects are disorder-induced owing to the statistical occurrence of the Si atoms within the regular hexagonal Te sublattice. © 1976 Springer-Verlag.