The Electricity Reliability Council of Texas says electricity consumers used an hourly average of 63,453 megawatts of power between 4 and 5 p.m. July 13.
That beat the previous record of 62,786 megawatts set last July 8.
Before that, the record day had been August 17, 2006, when ERCOT consumers used 62,339 megawatts.
ERCOT is the electric grid operator for much of the state.
ERCOT officials said they expected continued high electricity demand the entire week.
July 13 was the hottest day so far this summer in many Texas locations, with temperatures reaching as high as 107 in north and northwest of Fort Worth in the towns of Bridgeport and Graham.