A theoretical study based on first-principle band-structure calculations is carried out for the hypothetical semi-Heusler alloys NiVM (M=P, As, Sb, S, Se, and Te). For all compounds it is found that the ferromagnetic state is more favorable than the paramagnetic state. NiVAs is predicted to be a half-metallic ferromagnet with a small half-metallic gap of 0.07 eV and an integer magnetic moment of 2 μB, and NiVP and NiVSb are so-called nearly half-metallic ferromagnets. Furthermore, we find a clear indication that the substitution on the sp atoms influences the hybridization between Ni and V atoms, and can even destroy the half metallicity.