Bill Gates on Thursday ruled out ever returning to the helm of Microsoft while dismissing criticism by late Apple founder Steve Jobs, who he called "brilliant".

Gates, in Sydney for a family holiday, said recent rumours that he was considering a full-time comeback to the US software giant he founded, but stepped back from in 2006, were untrue.

In an interview with the Sydney Morning Herald, he said he was busy working with the Bill & Melinda Gates Foundation "and that will be what I do for the rest of my life".

"I'm part-time involved with Microsoft, including even being in touch this week to give some of my advice, but that's not going to change -- the foundation requires all of my energy and we feel we're having a great impact."

The foundation funds health and anti-poverty projects in developing countries, including malaria research and vaccination programmes, and works with the poor in the United States.

Steve Ballmer, who took over from Gates, has been criticised by some for lacking the innovation that Gates brought to the company.

Gates has also faced his share of criticism, with Apple innovator Jobs portraying the Microsoft founder as "basically unimaginative" and an exploiter of other people's ideas in an authorized biography.

Gates maintained a long rivalry with Jobs, who died from cancer in October, and said the Apple boss was hard on Microsoft because "the Microsoft machines outsold his machines by a lot".

"But that's fine, he was a brilliant person," he added to the newspaper.

"Our work at Microsoft was super successful for all good reasons, but Steve made huge contributions and he actually in his last few years was a lot kinder than that. But over the years he did say some tough things."