Ground-state structures of semiconductor-alkali binary anions E(n)A(-) (E=Ge, Si; A=K, Na, Li; n=1-10) have been optimized using the second-order Moller-Plesset perturbation (MP2) method and their vertical detachment energies predicted employing the outer valence Green's function (OVGF) procedure. The calculated lowest detachment energies of E(n)A(-) anions composed of E-n(2-) semiconductor Zintl anions and face-capping or edge-bridging A(+) alkali cations exhibit maximums around n=2, 5, 9, and 10 and minimums at n=3 and 7, in overall agreement with the magic numbers observed for GenK- in time-of-flight mass spectroscopy. The lowest detachment energies of E(n)A(-) series increase from A=K, Na, to Li with increasing electronegativities of the alkali atoms and decreased E-A ionic bond lengths. Small ternary GemSinK- (m+nless than or equal to6) exhibit similar behavior to binary EsK- at the same sizes (s=m+n). (C) 2003 American Institute of Physics.