The first-order Stark effect occurs in rotational transitions of symmetric top molecules (but not for linear and asymmetric molecules). In first approximation a molecule may be seen as a rigid rotor. A symmetric top rigid rotor has the unperturbed eigenstates | J K M ⟩ ⟩ = ( D M K J ) ∗ ∗ with M , K = − − J , − − J + 1 , … … , J with 2(2 J +1)-fold degenerate energy for |K| > 0 and (2 J +1)-fold degenerate energy for K=0. Here D MK is an element of the Wigner D-matrix. The first-order perturbation matrix on basis of the unperturbed rigid rotor function is non-zero and can be diagonalized. This gives shifts and splittings in the rotational spectrum. Quantitative analysis of these Stark shift yields the permanent electric dipole moment of the symmetric top molecule.