In a large bowl, combine soy sauce, sugar, garlic, oil, pepper and salt. Apply this moist rub to the chicken with your fingers until it is well coated, then set aside for 30 minutes. Preheat the grill or broiler, positioning a rack about 6 inches from the heat. Grill or broil the chicken from 25 to 30 minutes, turning occasionally, until golden brown and cooked through. Serve hot.