Mix brown sugar, soy sauce, sesame seeds, sherry, ketchup, garlic powder, and ginger together in a bowl.
Place chicken thighs in the bottom of a slow cooker. Pour sauce over top.
Cover and cook until chicken is no longer pink in the center and juices run clear, on Low, 6 to 8 hours, or High, 3 to 4 hours. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).