Abstract: Assistive orthotics have the potential to augment the grasping capabilities of individuals with limited hand functionality. People with a cervical-level spinal cord injury (SCI) lack direct control of semi-flaccid, curled fingers on both hands, which often precludes independent donning and doffing of orthotics, thus limiting their use in daily life. This paper presents a novel orthotic designed to improve hand functionality while facilitating independent daily use for individuals with cervical SCI: the Single-size Semi-soft Assistive Mitten (SSAM). This device utilizes a slim dorsal leaf spring and underactuated cable drive to passively open and actively close the hand, in a way that is robust to variations in hand size. This mitten is intended to improve ease of donning and doffing, as the device is attached to all fingers at once. A prototype is developed based on simulation studies, and grasping performance of the proposed design is validated with five healthy subjects. Successful grasping trials, along with positive user feedback, suggest that the SSAM has a comfortable and intuitive design for long-term, independent use and will enable future studies into feasibility of daily use for people with SCI.