This study reports the linear and nonlinear optical and electronic properties of as-prepared and annealed ∼240 nm thick Ge₂₀Te₈₀ films. The optical properties were studied based on the transmittance and reflectance spectra measured by spectrophotometer within the range of 380–1090 nm. The optical absorption data were described by Tauc’s relationship. The refractive index and extinction coefficient were evaluated, and a correlation between the refractive index and the optical bandgap is discussed. The dispersion and oscillator energies were analyzed by the Wemple-DiDomenico concept of the single oscillator. The dielectric constants, the loss tangent, and volume/surface energy loss functions were deduced. The electronic polarizability was computed by three different methods. The optical bandgap of thermally evaporated Ge₂₀Te₈₀ film and films annealed at 373–473 K (amorphous films) exhibit allowed direct and indirect transitions while the films annealed at 523–573 K (crystalline films) exhibits only allowed direct transition. The developments of crystal structure, optical parameters, and the optical conductivity upon thermal annealing, make the Ge₂₀Te₈₀ chalcogenide film candidates for numerous photonic applications.