An electrode assembly for use in combination with an electrosurgical instrument having opposing end effectors and a handle for effecting movement of the end effectors relative to one another. The electrode assembly includes a housing having one portion which is removably engageable with the electrosurgical instrument and a pair of electrodes each having an electrically conductive sealing surface and an insulating substrate. The electrodes are removably engageable with the end effectors of the electrosurgical instrument such that the electrodes reside in opposing relation relative to one another. The dimensions of the insulating substrate are different from the dimensions of the electrically conductive sealing surface to reduce thermal spread to adjacent tissue structures.