The presence of the sulfonium ion (H₃S⁺) was sought via its 1₀-0₀ rotational transition at 293.4572 GHz toward a number of sources by Neufeld et al. using the Institut de Radioastronomie Millimétrique (IRAM) 30m telescope on Pico Valeta in southern Spain. Four other sulfur-containing molecules were successfully detected by the study: SH, H₂S, CS, and SO. The five objects where H₃S⁺ was searched for include the star-forming regions W31C, G29.96-0.02, G34.2+0.1, W49N, and W51. The upper limit derived for H₃S⁺ relative to H₂S—τ(H₃S⁺)/τ(H₂S)—was about 0.01. The 1₀-0₀ rotational transition of H₃S⁺ was measured by Saito et al. in 1987.

Sulfonium or protonated hydrogen sulfide is analogous to the known astromolecule, hydronium, H₃O⁺. Both compounds are pyramidal. In organic chemistry, sulfonium is also the generic term for any tricoordinated sulfur cation (SR₁R₂R₃)⁺. A large number of sulfonium salts have been characterized.