The adsorption and thermal decomposition of N2H4 and CH3N2H3 on Si(111)7 × 7 were investigated using XPS, UPS and HREELS in the 120-1350 K surface temperature range. Both molecules were partially dissociated into N2Hx or CH3N2Hx (x=2, 3) species with the N-N bond parallel or nearly parallel to the surface as they adsorbed on the surface at 120 K, especially at lower dosages (e.g., < 0.2 L) and more so for N2H4 than CH3N2H3. This was evidenced by the appearance of the Si-H vibration at 255 meV in the HREEL spectra and by the relatively larger FWHMs of the N1s XPS and the n+, n- molecular UPS peaks. When a ∼0.4 L N2H4 or CH3N2H3 dosed sample was annealed to ∼500 K, significant desorption of the molecules occurred as well as further dissociation of the NH bonds. Above ∼600 K the NN bond began to break for both molecules. At ∼730 K, the CN bond dissociated to form CHx on the surface in the case of CH3N2H3. Further annealing of the sample caused complete cracking of the N-H and C-H bonds until Si3N4 or a mixture of Si-nitride and Si-carbide were formed for N2H4 or CH3N2H3, respectively.