The mainland of Alaska is not an island. It is a peninsula, as it's surrounded by water on three sides and land on the fourth side. The Eastern edge of Alaska borders Canada, while the Arctic Ocean is to the north and the Pacific Ocean to the west and south.
While the Alaskan mainland is a peninsula, there are 2,670 islands that are part of the state of Alaska. Many of Alaska's islands can be found within a few miles of the mainland. However, there is a long archipelago of islands extending southwest from the mainland into the Bering Sea.