ZURICH, April 23 (Reuters) - The Swiss National Bank made a loss of 500 million Swiss francs ($636.70 million) for the first quarter, the central bank said on Thursday, as gains in gold prices were cancelled out by declines in the value of its foreign currency holdings.

The SNB incurred a loss of 8.2 billion francs on its foreign currency holdings, triggered by a decline in the value of the shares and bonds it holds.

($1 = 0.7853 Swiss francs)

(Reporting by John RevillEditing by Ludwig Burger)