An apparatus for ablating tissue, the apparatus having first and second opposing jaws operative to compress tissue to be allayed therebetween, the first jaw having a first ablation surface directing ablative energy into the tissue and the second jaw having a second ablation surface reflecting incident ablative energy into the tissue. The ablative energy may be ultrasonic, microwave, cryoablation, radio-frequency, photodynamic, laser, and cautery energy. The instrument may also have a pointed tip for piercing tissue, allowing the instrument to clamp the tissue wall of a hollow organ before ablation. Alternately, the instrument may clamp two or more tissue layers of a hollow organ without piercing prior to clamping an ablation.