Shemya or Simiya (Aleut: Samiyax̂) is a small island in the Near Islands group of the Semichi Islands chain in the Aleutian Islands archipelago southwest of Alaska, at 52°43′27″N 174°07′08″E / 52.72417°N 174.11889°ECoordinates: 52°43′27″N 174°07′08″E / 52.72417°N 174.11889°E. It has a land area of 5.903 sq mi (15.289 km²), and is about 1,200 miles (1,900 km) southwest of Anchorage, Alaska. It is 4.39 kilometres (2.73 mi) wide and 6.95 kilometres (4.32 mi) long.
The Russian vessel Saint Peter and Paul wrecked at Shemya in 1762. Most of the crew survived.
A United States Air Force radar, surveillance, and weather station and aircraft refueling station, including a 10,000 ft (3 km) long runway, opened on Shemya in 1943 and is still in operation. The station, originally Shemya Air Force Base or Shemya Station, had 1,500 workers at its peak in the 1960s. Observations from Shemya were normally the first radar reports of new Russian satellite launches from Tyuratam (Baikonur) in the early days of satellite tracking; see Project Space Track.