AbstractStable acyclic arsenium cations R2As+, isoelectronic analogues of germylenes, are rare in comparison to the corresponding phosphenium cations. The first example of a diphosphaarsenium salt, [{(Dipp)2P}2As][Al{OC(CF3)3}4]⋅1 PhMe, is described. This salt exhibits remarkable stability due to the delocalisation of a lone pair from a planar phosphorus centre into the vacant p‐orbital at arsenic; the bonding in 2 has been probed by DFT calculations. An attempt to synthesise an analogous diphosphaphosphenium salt unexpectedly generated the cyclic phosphonium salt [cyclo‐{(Mes)P}2P(Mes)2][BArF4]⋅CyMe through the cyclisation of a putative phosphine‐substituted diphosphene cation intermediate.