The Gulf's largest utility by market value made SR2.32 billion ($618 million) in the three months to Sept. 30, compared with SR1.73 billion a year earlier, it said in a statement.

It was SEC's highest ever quarterly net profit since its inception 11 years ago.

Half of the net profit increase was generated by a hike in power tariffs for commercial, government and industrial users in July, Chief Executive Ali Saleh Al-Barrak told Reuters.

"The other 50 percent came from a 20 percent rise in power consumption during the third quarter which coincided with a super-hot summer season and the fasting month of Ramadan," Al-Barrak said.

The state-controlled company usually posts its best quarterly earnings during the second and third quarters of the year as hotter temperatures boost power consumption. But Al-Barrak said the impact from the new tariffs for some users is set to replicate itself in the upcoming two quarters. The new tariffs were introduced on July 1.

The firm made a net loss of SR782 million in the first quarter of 2010 and SR510 million in the fourth quarter of 2009.

The tariff hike was the latest government-sponsored step to help the power utility cope with power demand growing at an annual 8 percent and requiring investments close to $80 billion between 2008 and 2018.

Strongly outperforming the all-share and other sector indexes, shares in the firm have gained about 33 percent this year, with much of the advance made after the announcement of the higher tariffs.

The government granted the cash-strapped firm a SR15 billion soft loan in April to support its finances and ease the burden of lending from commercial banks.