Hawking taught at Cambridge from 1977 until his death. He held positions as professor of gravitational physics, research director at Cambridge’s department of applied mathematics and theoretical physics, and spent 30 years as the Lucasian Chair of Mathematics at Cambridge. He first obtained the position of Lucasian in 1979, when he was just 27 years old, and retired from it in 2009.
It’s not clear how much money Hawking made in these positions, but in 2014 the average Cambridge professor was making around £70,000 (or $98,000) annually according to the Times Higher Education. However, during the 1970s and '80s, a lengthy and fascinating article in Vanity Fair says Hawking only made about $25,000 a year a university fellow.
Given Hawking’s fame, it’s safe to say he made significantly more than that as his fame increased exponentially. Cambridge advertised a job for an assistant to Hawking in 2011 which paid £25,000 a year — about $40,000 at the time.