Supersymmetric Grand Unified Models without Adjoint Higgs Fields

We discuss two classes of supersymmetric grand unified theories based on extended gauge groups $SO(10) \times SO(10)$ and $SO(10)\times SO(10)\times SO(10)$. Effective adjoint fields of each gauge group SO(10) are argued to be formed from combining two Higgs fields in fundamental representation of the extended gauge groups, one obtaining its VEV along the diagonal $SO(10)_D$ direction and the other acquiring its VEV along the diagonal $SU(5)_D\times U(1)_D$ or its subgroup direction. Thus experimentally acceptable fermion mass matrices, such as Georgi-Jarlskog ansatz, with successful GUT mass relations can be constructed in these theories.