score:12
The next island east of Semisopochnoi Island (longitudinally) is Amatignak Island which is at 179° 6' 31" W.
Wikipedia says
The southernmost point of Alaska is on this island, as well as the westernmost longitude of Alaska, the United States, and North America.
The International Date Line passes to the west of Attu, so Amatignak is further away from that than Attu or Semisopochnoi.