The method involves introducing an implantable sensor (112) into a package (114), where the package seals the implantable sensor from bacteria and accommodates a radiation shield (144) that shields an electronics part. The implantable sensor in the package is irradiated from irradiating direction (146) with electron radiation. The radiation shield shields an electronic component (128) of the electronics part from the irradiating radiation. The radiation shield is arranged by a sensor part (120) that is sterilized by the irradiating radiation. An independent claim is also included for a sterilizing device for sterilizing an implantable sensor for sensing analyte in body tissue.