One person with direct knowledge of the matter told Reuters the expansion was in response to a request from the U.S., but declined to provide further details.
"The United States requested it. Internally TSMC is planning to build up to six fabs," the person said, adding that it was not possible to give a timeframe.
A second person familiar with the plans said the company had already made sure there was enough space for expansion when they obtained the land for the first plant.
"It's so they can build six fabs," the source said.
The third person, from a TSMC supplier involved in the Arizona project, said TSMC had told them the plan was to build a total of six fabs over the next three years.