A non-charge-sheet based analytic theory for undoped symmetric double-gate MOSFETs is presented in this paper. The formulation is based on the exact solution of the Poisson's equation to solve for electron concentration directly rather than relying on the surface potential alone. Therefore, carrier distribution in the channel away from the surface is also taken care, giving a non-charge-sheet model compatible with the classical Pao-Sah model. The formulated model has an analytic form that does not need to solve for the transcendent equation as in the conventional surface potentials or Pao-Sah formulation. The validity of the model has also been demonstrated by extensive comparison with AMD double-gate MOSFET's data.