Neptunium silicide is a binary inorganic compound of neptunium and silicon with the chemical formula NpSi
₂.^[1] The compound forms crystals and does not dissolve in water.^[2]

Heating neptunium trifluoride with powdered silicon in vacuum:^[3]

${\displaystyle \mathsf{4}\mathsf{N}\mathsf{p}{\mathsf{F}}_{\mathsf{3}}\mathsf{+}\mathsf{11}\mathsf{S}\mathsf{i}\stackrel{{\mathsf{1500}}^{\mathsf{o}}\mathsf{C}}{\to }\mathsf{4}\mathsf{N}\mathsf{p}\mathsf{S}{\mathsf{i}}_{\mathsf{2}}\mathsf{+}\mathsf{3}\mathsf{S}\mathsf{i}{\mathsf{F}}_{\mathsf{4}}}\{\backslash displaystyle\; \{\backslash mathsf\; \{4NpF\_\{3\}+11Si\backslash \; \backslash xrightarrow\; \{1500^\{o\}C\}\; \backslash \; 4NpSi\_\{2\}+3SiF\_\{4\}\}\}\}$

Neptunium silicide forms crystals^[4] of tetragonal crystal system, space group I4₁/amd, cell parameters: a = 0.396 nm, c = 1.367 nm, Z = 4.^[5]

Neptunium disilicide does not dissolve in water.

Neptunium disilicide reacts with HCl:^[3]

NpSi₂ + 8HCl → NpCl₄ + 2SiH₄