  In certain five dimensional gauge theories the Standard Model Higgs doublet
is identified, after compactification on the orbifold S^1/Z_2, with the zero
mode of the fifth component of the gauge field. An effective potential for the
Higgs field is generated via quantum corrections, triggered by the breaking of
the underlying gauge symmetry through boundary conditions. The quartic Higgs
coupling can be estimated at low energies by employing the boundary condition
that it vanishes at the compactification scale \Lambda, as required by five
dimensional gauge invariance. For \Lambda \gtrsim 10^{13}-10^{14} GeV, the
Standard Model Higgs boson mass is found to be m_H = 125 \pm 4 GeV
corresponding to a top quark pole mass M_t = 170.9 \pm 1.8 GeV. A more complete
(gauge-Higgs-Yukawa) unification can be realized for \Lambda ~ 10^8 GeV, which
happens to be the scale at which the SU(2) weak coupling and the top quark
Yukawa coupling have the same value. For this case, m_H = 117\pm 4 GeV.
