SOUTH PORTLAND — National Semiconductor says its plant in Maine will continue operating after Texas Instruments Inc. completes its acquisition of the company.

The two companies announced Monday that Texas Instruments, based in Dallas, will purchase California-based National Semiconductor in a deal valued at $6.5 billion.

In announcing the deal, the companies said Texas Instruments will continue to operate National Semiconductor’s manufacturing plants in South Portland, Scotland and Malaysia.

The South Portland plant opened in 1997 and employs about 550 people.