National Semiconductor Corp plans a near doubling of its investment in Singapore, one of its eight manufacturing sites worldwide, where it has invested about $136m so far, including an $8m extension of its semiconductor plant, just opened. Output, currently running at $800m a year, is expected to hit $1,000m next year as a result of the expansion. It plans to invest $130m more over the next five years to upgrade technology and equipment for the plant, which employs 1,800.Separately, NatSemi was ordered to pay a $50,000 fine and do $445,000 of modifications in Santa Clara to meet US Clean Water Act standards.