University of KwaZulu-Natal physics professor Nithaya Chetty has handed in his resignation and is preparing to take up a post at another university in the country.

Chetty's resignation comes four months after he and mathematics professor John van den Berg were charged for criticisms made in the media of university vice-chancellor Malegapuru Makgoba.

In a letter to colleagues and friends on Wednesday, Chetty said his resignation had come after much consideration and a decision to do what was best for him and his family.

"This has taken a huge toll on ourselves and our loved ones," he said.

He made special mention of Van den Berg.

"I have enormous respect for John's courage and integrity, and I think that John now needs to be given the opportunity and the support to get back to his normal life in peace and quiet," he said.

Chetty said he had been offered a physics academic position at a top South African university, to start in January.

He had also been invited to deliver the 2009 T B Davie Academic Freedom lecture at the University of Cape Town.

This year he was elected to the International Union for Pure and Applied Physics at the Commission on Computational Physics in Japan.

Among other accolades, he has also been invited to be guest editor of a special issue of an American journal and he has served as national president of the South African Institute of Physics.

Jane Duncan, of the Freedom of Expression Institute, said: "I think he was forced into a position where he felt he had to resign. The disciplinary process, with such expensive legal counsel, was set up so that the professors would lose."