Preheat broiler. Rinse chicken thighs; pat dry. Arrange thighs, skin side down, on a broiler pan. In a small bowl, combine lemon juice, olive oil, rosemary and garlic. Brush 1/3 of mixture over chicken and sprinkle with salt and pepper. Broil 4 to 6 inches from heat until lightly browned, about 7 minutes.
Using tongs, turn chicken thighs skin side up. Brush 1/3 of lemon-juice mixture over skin and sprinkle with salt and pepper. Broil until thighs are browned, about 7 minutes.
Turn off broiler and set oven to 450°F. Brush final 1/3 of lemon-juice mixture over chicken (discard any leftover lemon-juice mixture) and return pan to oven. Bake until juices run clear when pricked with a fork and meat is no longer pink at the bone, about 10 minutes. Serve hot.