  According to Mumford's geometric invariant theory, the moduli space of stable
cubic fivefolds is compactified by adding nonstable semi-stable (i.e., strictly
semi-stable) locus. In this paper, we prove that this locus consists of 21
irreducible components. Moreover, we give a description of equation and
singularity of the cubic fivefold corresponding to the generic point in each
component.
