We study the dynamical symmetry breaking in the gauge-Higgs unification of the 5D N = 1 SUSY theory, compactified on an orbifold, S¹/₂. This theory identifies Wilson line degrees of freedoms as ``Higgs doublets''. We consider SU(3)<sub>c</sub> × SU(3)<sub>W</sub> and SU(6) models, in which the gauge symmetries are reduced to SU(3)<sub>c</sub> × SU(2)<sub>L</sub> × U(1)<sub>Y</sub> and SU(3)<sub>c</sub> × SU(2)<sub>L</sub> × U(1)<sub>Y</sub> × U(1), respectively, through the orbifolding boundary conditions. Quarks and leptons are bulk fields, so that Yukawa interactions can be derived from the 5D gauge interactions. We estimate the one loop effective potential of ``Higgs doublets'', and analyze the vacuum structures in these two models. We find that the effects of bulk quarks and leptons destabilize the suitable electro-weak vacuum. We show that the introduction of suitable numbers of extra bulk fields possessing the suitable representations can realize the appropriate electro-weak symmetry breaking.