A 2-D semianalytical model using the Legendre polynomial approach was applied for modeling the piezoelectric transformer (PT). In the model, the mechanical displacements and the electric potential were expanded in a double series of orthonormal polynomials with an appropriate analytical form. Series and parallel resonance frequencies, input electrical admittance, and voltage gain were obtained for the PT. The results are in excellent agreement with both the numerical results calculated with a 3-D finite-element analysis and experimental ones. The approach is able to predict the behavior of a wide and a long PT.