The Semidi Islands are a group of islands of the state of Alaska, United States, lying offshore in the Gulf of Alaska. The islands are part of Kodiak Island Borough and are located southwest of Kodiak Island, about halfway between the Alaska Peninsula mainland and Chirikof Island. The largest islands of the group are Aghiyuk Island and Chowiet Island. The island group has a total land area of 30.178 km2 and is uninhabited. They are part of the Alaska Peninsula unit of the Alaska Maritime National Wildlife Refuge.