SOUTH PORTLAND — Fairchild Semiconductor, a South Portland-based manufacturer of silicon chips for electronics, announced today that about 120 staffers will be laid off in the next nine months as part of the restructuring plan announced in mid-December.

In a media release, Fairchild said it will close its 6-inch manufacturing line at the Western Avenue site in South Portland and transfer production to a more modern 8-inch line at the same site. The move and the job cuts, said the company, will improve productivity, lower operating costs and boost return on assets.

“We regret having to make these difficult decisions that affect our community and our friends,” said Fairchild Vice President and Managing Director Benny Chang in a prepared statement. “Our goals are to make Fairchild in South Portland highly cost competitive and to build a foundation for sustainable future growth.”

The restructuring and expected layoffs were announced in December. At the time, Fairchild spokeswoman Patti Olson said the decision to cut staff was made by local managers after an evaluation of the plant’s expected 2011 output.

The company faces competition from other chip manufacturers in the United States, Asia and elsewhere.

Fairchild’s silicon chips are used in cell phones, automobiles, electronics and a host of other consumer products and are shipped worldwide.

The company employs about 800 workers in Maine.