The utility of surface-enhanced Raman scattering (SERS) fur characterizing phonon and related interfacial vibrations within ultrathin semiconductor layers on gold substrates is demonstrated, specifically for cadmium chalcogenide (CdSe, CdS) films formed by electrochemical atomic layer epitaxy. The occurrence of quantum-confinement effects for CdSe films less than ca. 10 monolayers thick is clearly evident from the observed ca, 12 cm(-1) phonon redshifts and bandshape changes. Milder phonon redshifts are seen for the ultrathin CdS films, suggesting the presence of offsetting blueshifts from lattice compression. The observed sensitivity of the phonon spectra to the order of initial Cd/Se or Cd/S monolayer electrodeposition, along with the retention of An-Se and Au-S vibrational bands upon layer growth, signal the importance of the initial chemisorbate to the epitaxial film structure and vibronic properties.