  In orbifold models, gauge, Higgs and the matter fields can be unified in one
multiplet from the compactification of higher dimensional supersymmetric gauge
theory. We study how three families of chiral fermions can be unified in the
gauge multiplet. The bulk gauge interaction includes the Yukawa interactions to
generate masses for quarks and leptons after the electroweak symmetry is
broken. The bulk Yukawa interaction has global or gauged flavor symmetry
originating from the R symmetry or bulk gauge symmetry, and the Yukawa
structure is restricted. When the global and gauged flavor symmetries are
broken by orbifold compactification, the remaining gauge symmetry which
contains the standard model gauge symmetry is restricted. The restrictions from
the bulk flavor symmetries can provide explanations of fermion mass hierarchy.
