A method of forming a harmonic-effect-suppression structure is disclosed. The method includes: providing a semiconductor substrate having a base semiconductor substrate, a buried dielectric on the base semiconductor substrate, and a surface semiconductor layer on the buried dielectric. Next, a deep trench is formed extending through the surface semiconductor layer and the buried dielectric into the base semiconductor substrate, a silicon layer is formed within a lower portion of the deep trench, the silicon layer allowed to have a top surface height substantially the same as or lower than a top surface height of the base semiconductor substrate, and a dielectric layer is formed within the deep trench and on the silicon layer.