It was not immediately clear how much Toshiba was planning to invest. However, it marks the two Japanese companies' first joint project since Rohm decided to invest a total of 300 billion yen ($2 billion) to join a $14 billion buyout of Toshiba.

It also gives a glimpse of Toshiba's business plan following the delisting of its shares, scheduled for Dec. 20.

Toshiba and Rohm will receive subsidies of about 120 billion yen to 130 billion yen from the Japanese government designed to help promote the domestic semiconductor industry, said the sources, who declined to be identified as the matter is private.

The plan will be announced later this month, the sources added.

Rohm's new plant, to be built in Miyazaki Prefecture in the southern island of Kyushu, will mainly produce silicon carbide power chips, which have been gaining traction with electric car makers as they can handle high voltages and are more power efficient.

A Toshiba spokesperson said nothing has been decided at this point. A Rohm spokesperson declined to comment.

(Reporting by Miho Uranaka and Makiko Yamazaki; Editing by David Dolan and Mark Potter)

By Miho Uranaka and Makiko Yamazaki