The dissociation thermochemistry of tetramethylsilane cation was investigated by two new methods, threshold collision-induced dissociation (CID) and zero-pressure thermal infrared radiation-induced dissociation (ZTRID). For the loss of a methyl group from SiMe(4)(+), the two methods gave 0 K bond dissociation energies of 0.72 eV (CID) and 0.67 eV (ZTRID). These values were supported by an indirect thermochemical calculation and by an ab initio (MP2) bond strength calculation. A best value for this bond strength of 0.69 +/- 0.06 eV is assigned. From the CID measurements, further bond strengths were assigned for SiMe(2)(+)-Me (5.32 +/- 0.28 eV), SiMe(+)-Me (1.27 +/- 0.50 eV), and Si+-Me (4.29 +/- 0.06 eV). New or reevaluated heat of formation values are given for the SiMe(x)(+) species (x = 0-4).