National Semiconductor, one of the world's largest manufacturers of computer components, yesterday reported a loss for its fiscal first half, which it linked to reduced demand and lower prices for semiconductors.

The company, which is based in Santa Clara, Calif., said it lost $88.3 million in the six months that ended Dec. 15. Last year, the company made a profit of $44.4 million in the same period.

For the second quarter, the firm reported a loss of $34.8 million compared with net earnings of $8.5 million in the same period of 1984.

Sales for the fiscal 1986 quarter fell to $359.4 million from $435.4 million in the previous year's quarter. Per-share earnings in the 1985 quarter amounted to 10 cents a share.

Sales for first half of fiscal 1986 were $782.7 million, with a net loss of $88.3 million ($1.01 a share) compared with sales of $964.4 million and earnings of $44.4 million (50 cents) a year earlier.

National Semiconductor's misfortunes reflect the dramatic falloff in personal-computer sales over the last 18 months, according to Blake Childs, a securities analyst with Bateman Eichler, an investment brokerage company. He said personal-computer sales started to fall in June 1984 as the initial demand began to dry up. However, "unrealistic sales expectations" resulted in a buildup in inventories, he said.

Consequently, the market in semiconductors -- such as microchips -- crashed, and a number of companies were forced to close plants, Childs said.

National Semiconductor said more orders had been received by its semiconductor division, resulting in more of a backlog than in any quarter since fiscal 1984.