In this work, Gallium Arsenide (GaAs) films growth via Close Space Vapor Transport (CSVT) technique on n-type Silicon (Si) substrates (100) and its nitridation effect in the ammonia ($N{H}_3$) environment is reported. The GaAs films were grown at 800, 900, and 1000 ${}^{\circ }$C, and the nitridation process was carried out at 900 ${}^{\circ }$C with an $N{H}_3$:$H_2$ gasses ratio. The GaAs films with and without nitridation process were analyzed using X-ray diffraction (XRD), Raman spectroscopy, Diffuse Reflectance Spectroscopy, and Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX). Grazing incidence X-ray diffraction measurements of GaAs films nitrided confirm a polycrystalline GaN wurtzite structure with preferential orientation along (002), and additionality, a crystallographic plane (310) of low intensity is observed in $2\theta =52.{18}^{\circ }$ corresponding to $G{a}_2{O}_3$. The average quantification results in weight (Wt. %) of GaAs films nitrided was determined by EDS; Ga∼79, N∼17.1, O∼2 and As∼1.8 Wt. %. The presence of GaN, $G{a}_x{O}_y$, Si, and GaAs modes were found by Raman measurements, demonstrating a partial nitriding. The band gap estimation by diffuse reflectance was between 3.2 and 3.38 eV such values are close to that reported for bulk GaN (3.4 eV). The presence of oxygen in the structure could be related to substrates or the GaAs source.