We have performed a global structure optimization for Si8H8 cluster using a genetic algorithm (GA) coupled with an efficient and accurate tight-binding (TB) potential to describe the energies of the clusters. Structure models selected from the GA/TB optimization are further verified by ab initio calculations. Our study shows that a new structure with C-2 symmetry is energetically more stable than the octasilacubane structure previously proposed for Si8H8. This is in contrast to Ge8H8 where the octasilacubane structure is energetically more stable than the new G structure. Vibration and electronic properties of the new Si8H8 structure have also been studied. (C) 2003 Elsevier B.V. All rights reserved.