La2O3 films are obtained by annealing in vacuum La(OH)3 layers produced upon air exposure of La2O3 layers grown using atomic layer deposition. Sample thickness determines whether hexagonal or cubic La2O3 form. The observed infrared active phonon mode with minimum frequency for hexagonal La2O3 films is located at 198cm−1, in good agreement with the first principles calculations, and at a lower frequency than the corresponding mode for cubic La2O3 is at 235cm−1. Accordingly, electrical measurements reveal a dielectric constant around 27 for hexagonal La2O3 films, significantly higher than the one around 17 derived for cubic La2O3 layers.