The first bowl-shaped oligosilane, hexadecamethyldecasilahexahydrotriquinacene (1), and a related oligosilane, hexadecamethyldecasilaisotwistane (2), were synthesized, and their structures and properties were studied. The results revealed importance of sigma conjugation on a. bowl surface:. the HOMOs of 1 are sigma orbitals delocalized on the bowl surface, whereas the LUMO is a pseudo pi* orbital on the convex and concave sides of the bowl surface.