Disproportionation reactions of chlorosilane compounds in the presence of boron trichloride yield the compound H[B(SiCl3)(4)]. Spectroscopic analyses of the yellow-whitish solid with IR-, Raman-, and NMR-spectroscopy (Si-29, B-11) show the presence of a highly symmetric anion containing boron, which is fourfold coordinated with silicon. Due to the high symmetry (1)J(B-11,Si-29) and even (1)J (B-10, Si-29) couplings can be observed in the NMR spectra of the dissolved compound. The crystal structure analysis with a crystal obtained from toluene solution proves the existence of a highly symmetric borate anion, which is stabilized by four trichlorosilyl groups. The molecular structure consists of a para-protonated toluene cation and the weakly coordinating borate anion [B(SiCl3)(4)](-). Quantum chemical analysis of the tetrakis(trichlorosilyl)borate ion shows a negatively charged boron atom and the presence of polar Si-Cl and Si-B bonds. Highly reactive compounds [E(SiCl3)(n)](-) which are stabilized solely by trichlorosilyl groups have been prepared with E=C, Si, Ge, P, S in recent years. The superacid H[B(SiCl3)(4)] represents a new member in this elusive compound family.