An electrosurgical resection instrument for applying to biological tissue radiofrequency electromagnetic energy has a protective hull comprising a shaped piece of dielectric material mounted to cover an underside of an instrument tip of the instrument. The protective hull acts as a shield to protect tissue that may lie under the instrument tip from damage during treatment. The instrument may be particularly useful in procedures performed in a gastrointestinal tract, where bowel perforation is a concern, or in the pancreas, where damage to the portal vein or the pancreatic duct may occur when a tumor or other abnormality is being resected, dissected or removed.