What is the approximate temperature of the supergiant betelgeuse?

The approximate temperature of the supergiant Betelgeuse is of 3,590º K, 6,000º F or 3,320º C.

Betelgeuse is a semi-regular variable star of the red supergiant type, in the constellation Orion, located at a distance of about 500 light years from Earth.  

With a radius of around 1000-times the one of the Sun, Betelgeuse is a red supergiant, one of the largest stars known. When it explodes in a supernova, it will be visible from Earth in broad daylight for several days, with a brightness comparable to the Moon.