Amorphous GaN1−xAsx layers with As content in the range of x = 0.1 to 0.6 were grown by molecular beam epitaxy on Pyrex glass substrate. These alloys exhibit a wide range of band gap values from 2.2 to 1.3 eV. We found that the density of the amorphous films is ∼ 0.8–0.85 of their corresponding crystalline value. These amorphous films have smooth morphology, homogeneous composition, and sharp well defined optical absorption edges. The measured band gap values for the crystalline and amorphous GaN1−xAsx alloys are in excellent agreement with the predictions of the band anticrossing model. The high absorption coefficient of ∼ 105 cm−1 for the amorphous GaN1−xAsx films suggests that relatively thin films (on the order of 1 μm) are necessary for photovoltaic application.