What was the name of the first university where Einstein became a professor?

The first university where Einstein became a professor was the University of Zurich.

Einstein initially held a junior teaching position at the University of Bern in 1908, but that was not a full professorship. In 1909, after a well-received lecture on relativistic electrodynamics, the University of Zurich recruited him as an associate professor. He therefore became a university professor there before later appointments elsewhere.

In 1911, Einstein moved to the German Charles-Ferdinand University in Prague, where he held a full professorship. He returned to Zurich in 1912 to take a chair in theoretical physics at the Swiss Federal Polytechnic, now ETH Zurich. That later institution is a frequent source of confusion because Einstein studied and eventually taught there.

The University of Bern is also a tempting answer because it employed him first as a lecturer. University of Berlin came later, in 1914. The wording “became a professor” distinguishes Zurich from these earlier or later stages of his academic career.