The gas-phase decomposition pathways of TEG at CVD conditions for deposition of gallium phosphide, 400-675 °C and 5000 Pa, has previously been studied by quantum chemical calculations. It was then found that TEG has two decomposition pathways in the gas phase: β-hydrogen elimination of C2H4 and H2 assisted elimination of C2H6. Both pathways eliminates one ethyl ligand and replaces it with a hydrogen atom on the gallium atom. The β-hydrogen elimination of the first ethyl ligand is thermodynamically favored at 400 °C while further β-hydrogen eliminations of the other two ethyl ligands are not favored at 400 °C, but are favored at 500 °C. The H2 assisted elimination of C2H6 is thermodynamically favored for all three ethyl ligands already at 400 °C.