The mains power went off from 11:06 a.m. to 6:23 p.m disrupting the 40nm production line.
Although the diesel UPS kicked in, there was a short interruption in power supply and a voltage drop.
TrendForce reckons it will take 2-7 days to recalibrate the fab tools. It estimates the revenue hit at $10-15 million or 0.1% of total TSMC sales.
The fab runs the 40nm node which is used for automotive chips which have been in severe shortage for several months.
Customers most likely to be affected are NXP, Renesas and Sony.