An ansatz, Det. MH~=0, for the Higgsino mass matrix in string
orbifold trinification is suggested toward the minimal supersymmetric standard
model(MSSM). Small instanton solutions effective around the GUT scale can
fulfil this condition. An argument that the couplings contain a moduli field is
given for a dynamical realization of this Higgsino mass matrix ansatz.Comment: 15 pages of LaTeX fil