Homogenous aSi1-x Al x H y alloyed thin films, made by magnetron sputtering, has been found to exhibit tunable band gap and dielectric constant depending on their composition. The optical properties of alloys are largely defined by their electronic structure, which is is strongly influenced by interatomic charge transfer. In this work we have quantified interatomic charge transfer between Si, Al and H in aSi1-x Al x H y thin-films, with [Formula: see text] and [Formula: see text]. Charge transfer was found experimentally using x-ray photoelectron spectroscopy, by incorporating Auger parameter data into the Thomas and Weightman model. Both the perfect and imperfect screening models were tested, and the results were compared to models calculated using density functional theory based molecular dynamics. Using imperfect screening properties of Si and Al resulted in an excellent agreement between the experimental and computational results. Alloying aSi with Al is associated with donation of electrons from Al to Si for y = 0. For y > 0 electrons are transferred away from both Al and Si. The change in Si valence charge increases linearly with increasing band gap and decreasing dielectric constant. These relationships can be used as a quick guide for the evaluation of the Si valence charge and subsequently optoelectronic properties, at specific Al/Si ratios.