GaS, GaSe and GaTe are typical representatives of III-VI layered semiconductor materials, showing highly anisotropic mechanical and optical properties. At photon energies hv < E _g, the anisotropy ratio for the absorption coefficients at the n = 1 excitonic peak, corresponding to v E C and E °C polarizations, is α/α≈15. Optical functions n _e(λ) and n _o(λ) of GaS and GaSe in the wavelength range 0.36-22-m have been determined. For the photon energies hv <E ^ind _g , these correspond to a normal dispersion and can be described by power-law wavelength dependences. By means of FTIR transmission and reflection spectroscopy in the spectral range of 1000-85 cm ¹, for plan-parallel plates with thickness between several tens of nanometers and centimeters, the wavenumbers of longitudinal optical vLO and transverse optical v TOv phonons have been determined for GaSe [v(LO) = 254 cm ¹, cvTOv = 214 cm ¹], GaS [v(LO) = 359 cm ¹, v(TO) = 297 cm ¹, v(LO) =336 cm ¹], and GaTe [v(LO) = 164 cm ¹, v(TO) = 118 cm ¹].