The surface chemistry of Triallylamine (TAA), (C3H5)3N on Si(111) has been studied by adsorption under UHV conditions and in-situ characterization. High Resolution Electron Energy Loss Spectroscopy (HREELS) yields the spectrum of vibration modes at the surface, and X-ray Photoelectron Spectroscopy (XPS) yields the chemical bonding and the partial concentration of the different adsorbates in the near surface region. The tertiary amine TAA physisorbs at RT without dissociation. Successive annealing steps of the physisorbed phase induce the dissociation of the amine at 400 °C. At higher temperatures the allyl groups are partially desorbed and the rest fully dissociated at 600 °C, where the hydrogen leaves the surface and the nitrogen and carbon start to diffuse into the Si substrate. A very similar behaviour is observed for the adsorption of TAA on a heated Si substrate. The coadsorption with Triethylgallium (TEG) in the temperature range 500–800 °C does not induce significant changes in the reaction at the Si surface. A negligible quantity of Ga is detected at the surface after codeposition in the whole investigated temperature range. The growth of a GaN phase has not been observed, neither on Si(111) nor on Al2O3(0001) substrates.