Our previous study on GaN ALD from TEG used plasma-activated ammonia as the N precursor. Attempts to use thermally activated NH3 rendered very modest deposition of a film that was found to be mainly gallium oxide. Here, we used QMS to study a possible thermal ALD process with TEG and NH3. While it did not render any film for temperatures up to 400°C, we present mass spectra here to add to the process understanding. Mass spectrometry showed no C2H5 signal during the NH3 pulse, suggesting a decreased reactivity of the surface Ga species toward the NH3 half reaction. This means that less TEG can adsorb onto the surface after the NH3 pulse, which is in line with the lower intensity of the m/z = 29 signal after each full ALD cycle as shown in Fig. . Our results suggest that a thermal energy of up to 400 °C is not sufficient for the ligand exchange to occur when NH3 is pulsed into the reactor, however, plasma activation is needed, in line with our previous results on InN ALD.