We report on the uniform alignment and continuous ferroelectric switching of a twisted smectic C* liquid crystals (LCs). In contrast to surface stabilized ferroelectric LCs, a twisted smectic C* (Sm C*) structure exhibits essentially no threshold field and produces intrinsic gray scales. For constructing such a twisted structure, the symmetry in molecular tilt with respect to the rubbing axis is externally imposed by the surface forces. The symmetry required for producing a uniformly twisted structure is that the twist angle between two rubbing axes on the substrates must be exactly twice of the molecular tilt. One important parameter is the existence of the smectic A state in the phase sequence, which facilitates to the uniform growth of the smectic layers. We perform numerical simulations to obtain the director profiles and the resultant electro-optic modulation as a function of the electric field in the twisted Sm C* structure. It is found that the experimental data agree well with the numerical results.