The dissociation energy of SiO(g) has been determined mass spectrometrically by studying the isomolecular equilibrium Ge(g) + SiO(g) = GeO(g) + Si(g). Third-law calculations lead to ∆H298 = 26.6 ± 2 kcal/mole for the reaction, which yields D°0(SiO) = 182.8 ± 3 kcal/mole, or 7.93 ± 0.13 eV. The ionization potentials of SiO and GeO were measured and found to be 11.6 ± 0.2 and 11.5 ± 0.5 eV, respectively. Both of these ionization potentials are higher than previously published values. These data yield D°0(SiO+) = 4.5 ± 0.2 eV, in accord with the results of recent ion-neutral reaction studies. The relation of D°0(SiO) to the bonding in SiO is discussed briefly.