As the heaviest analogue of ammonia (a pnictogen hydride), BiH3 is unstable, decomposing to bismuth metal well below 0 °C.

[1] The term bismuthine may also refer to a member of the family of organobismuth(III) species having the general formula BiR3, where R is an organic substituent.

BiH3 is prepared by the redistribution of methylbismuthine (BiH2Me):[2] The required BiH2Me, which is also thermally unstable, is generated by reduction of methylbismuth dichloride, BiCl2Me with LiAlH4.

This test relies on the thermal decomposition of these trihydrides to the metallic mirrors of reduced As, Sb, and Bi.

[2] The low stability of BiH3 precludes significant health effects, it decomposes rapidly well below room temperature.