The arsonium salt [Ph3As-CH2-OTf]+ OTf- 11a contains a 1,1-biselectrophilic Csp3 center which permits to synthesize a wide range of symmetrical and unsymmetrical geminally bisonio-substituted methane derivatives. With neutral nucleophiles INu under mild condi- tions a series of 1.1-bisonium salts [Ph3As-CH2-Nu]2+ 2OTf- 12-23 is obtained in good yields. Under more stringent conditions the triphenylarsonio function in these salts can also be mobilized as a nucleofuge in a subsequent SN-reaction with a second nucleophile | Nu’, yielding a series of novel unsymmetrical 1,1-bisonium salts [Nu-CH2-Nu’]2+ 2OTf- 24-27. Structures 18, 23 and 26b were confirmed by X-ray analysis. For certain nucleophiles a discrete stepwise substitution of both nucleofuges in 11a cannot be realized and the corresponding symmetrical 1,1-bisonium salts (e.g. 28 and 30-32) are obtained directly. The experimental material can be rationalized on the basis of a simple MO model. The conclusion is that stabilization of a hypervalent SN2 transition state by an equatorial oniosubstituent parallels the stability of the underlying ylids. This is corroborated by model calculations. The geminal bisonium salts reported are potential precursors to mono- and 1,1-bisylids and, in special cases, to functional nucleophilic carbenes.