Rio Tinto has delivered a 12 per cent boost to its interim dividend despite a sharp slump in commodity prices and earnings, in a move than has seen the miner's net debt rise over the past six months.

Despite shareholders recently raising doubts about increasing debt to pay dividends, Rio maintained its policy of paying out half the previous year's dividend each August.

Shareholders will be paid $US1.075 per share, which is exactly half the $US2.15 full-year dividend paid for the 2014 calendar year and 12 per cent better than the $US0.96 interim dividend paid in August 2014.

For Australian shareholders, the dividend is 40 per cent higher than the one paid last August once fluctuations in the US dollar compared with the Australian dollar are taken into account.