Management at the Shinko Microelectronics plant in Tallaght officially confirmed this afternoon it would close at the end of November with the loss of 340 jobs.
The announcement followed meetings between the Tánaiste, and Minister for Trade, Enterprise and Employment, Ms Harney, and senior executives of the Japanese firm.
Ms Harney said the decision to close the semiconductor plant, which had been in operation for over 20 years, was a major blow to the jobs market, but insisted all had been done to prevent the closure.
"The company made every effort to find a purchaser for the facility, but the current market difficulties worked against them," she said.
Shinko, a joint venture between Fujitsu and Shinko Electronics, has had an operation in the Republic since 1980. It produces electronic components and memory semiconductors for the mobile phone market in Europe and Asia.
In 1999, it announced plans to invest £70 million in a new factory in Dublin but subsequently put these on hold.
The decision to close the Tallaght plant was taken as a result of the global economic slowdown, and the plant was being closed as part of a world-wide restructuring strategy, the company said today.
Ms Harney said her main priority was to try to find alternative employment for the redundant staff, and her Department would work in conjunction with FÁS to try to retrain workers.
She said Fujitsu had pledged to work with IDA Ireland to identify potential replacement investment in the Republic, and said she was confident those workers who had lost their jobs would receive a "generous severance package".
SIPTU said the news was "disappointing" and called for a high level task force to prevent the loss of future jobs and create new opportunities for the workers in Shinko.
"The negative effects that this decision will have on the employees, their families and the whole community in Tallaght cannot be understated," said Mr Brendan Byrne, SIPTU Electronics & Engineering Branch Secretary.
He added union officials would be meeting management on Monday to discuss redundancy payemnts.
Fujitsu employs nearly 600 people at its other facilities sited in Harcourt Street, Dublin, in Blanchardstown and Leopardstown, Co Dublin and in Dundalk, Co Louth.
Ms Harney said today she was confident these jobs were not at risk.
