Meltback etching, a deteriorating chemical reaction occurring between gallium and silicon under typical metal organic chemical vapor deposition growth conditions, is a common problem that often limits the development of GaN on silicon substrates, in particular, patterned substrates, and therefore must be circumvented. To further understand this reaction, energy dispersive X-ray spectroscopy was performed in cross-section, and a proposed 2-dimensional model on how meltback etching evolves throughout the growth process is discussed, which indicated an inter-diffusion reaction occurring primarily between gallium and silicon where gallium from GaN diffuses into the silicon substrate while silicon from the substrate diffuses out and incorporates into the GaN crystal. Moreover, we demonstrate an anisotropic behavior of the gallium penetrating the silicon substrate, which has shown to be delimited by the Si {111} planes. Finally, an approach to prevent meltback etching by changing the fractions of nitrogen and hydrogen in the carrier gas is presented and discussed. © 2017 Author(s).