The binary compounds ZnSb and ZnAs with the CdSb structure are semiconductors (II-V), although the average electron concentration (3.5 per atom) is lower than that of the tetrahedrally bonded III-V and II-VI archetype systems (4 per atom). We report a detailed electronic structure and chemical bonding analysis for ZnSb and ZnAs based on first principles calculations. ZnSb and ZnAs are compared to the zinc blende type semiconductors GaSb, ZnTe, GaAs, and ZnSe, as well as the more ionic, hypothetical, II-V systems MgSb and MgAs. We establish a clearly covalent bonding scenario for ZnSb and ZnAs where multicenter bonded structural entities (rhomboid rings Zn 2 Sb 2 and Zn 2 As 2 ) are connected to each other by classical two-center, twoelectron bonds. This bonding scenario is only compatible with a weak ionicity in II-V semiconductor systems and appears to be strongly coupled to the stability of the CdSb structure type. It is argued that a chemical bonding scenario with mixed multicenter and two-center bonding resembles that of boron and boron rich compounds, and is typical of electron poor spbonded semiconductors with average valence electron concentrations below 4 per atom.2