AbstractA theoretical study is made of the first‐order effects of an external electric field on optical transitions between strongly localized electronic states of isolated substitutional impurities in a wurtzite‐type crystal taking into account the near‐tetrahedral symmetry of these centers. The field effect on optical absorption bands due to A → T type transitions is treated on the basis of the method of moments which is extended to include mixing with the A ground level. The field‐induced changes of the zeroth and first moment (corresponding to changes in transition probability and to the Stark splitting, respectively) are calculated as functions of field and polarization direction. The polarization dependence of the zero‐field moments which is due to the axial part of the impurity potential is also discussed. On the basis of a rigid‐shift approximation a brief semi‐phenomenological treatment is given of the field‐induced changes in band shape.