The mass spectra of P4Se3, P4S3, P4S5, P4S7, and P4S10 are reported; all exhibit molecular ions, but are otherwise dominated by even-electron ions, especially PS+, P3S+, and P3S4+. P3S+ and P3S4+ may possess the P4 and P4S3 structures respectively, but with S+ replacing P. The only abundant odd-electron ions other than molecular ions are P2S5+ and P2S3+, observed in the spectrum of P4S10; this indicates dissociation of P4S10 into P2S5 molecules in the vapour phase, consistent with the reported vapour density. The spectra of frozen melts of composition P4S7–10 provide evidence for the presence of P4S9 molecules but not P4S8 molecules.