Gas-phase ion/molecule reactions in SiF4 were studied using a pulsed-electron beam mass spectrometer. The thermochemical stabilities of SiFm+(SiF4)(n) have been determined. Owing to the serious charging of the ion source, only up to n = 2 thermochemical data could be obtained experimentally. To evaluate bond energies that were difficult to obtain experimentally, ab initio calculations were carried out. Si+SiF4 and SiF+SiF4 have similar bond energies, 13 kcal/mol. SiF2+SiF4 and SiF3+SiF4 have 25 and 38 kcal/mol, respectively. While the bond energies of SiFm+(SiF4)(1) varied substantially with m, those of SiFm+(SiF4)(2) are all ca. 10 kcal/mol. The Si+SiF4 geometry is calculated to be a bidentate (bridged) one, where the Sif atom is located midway between two Si-F bonds. On the other hand, SiF3+SiF4 has a symmetric D-3d structure where an F atom is shared equally by two SiF3 fragments. Theoretical bond energies are in excellent agreement with experimental ones.