The crystal structures are related to those of ZnS with gallium in tetrahedral positions.

[3][2][4] The alpha and beta forms are isostructural with their aluminium analogues.

[5] The method of production can determine the polymorphic form produced, the reaction of Ga(OH)3 with H2S at different temperatures is reported to produce a different polymorph depending on the temperature, α- 1020 K, β- 820 K and γ- above 873 K [6] Ga2S3 decomposes at high temperature forming the non-stoichiometric sulfide, Ga4Sx (4.8 < x < 5.2).

[5] Ga2S3 dissolves in aqueous acids and decomposes slowly in moist air forming H2S.

[2] Ga2S3 dissolves in aqueous solutions of potassium sulfide, K2S to form K8Ga4S10 containing the (Ga4S10)8− anion which has an adamantane, molecular P4O10 structure.