The S&P 500 rose 0.50% to 1,417 in midday trading Thursday.
The Nasdaq was up 0.66% to 3,011, while the Dow Jones Industrial Average was up 0.36% to 13,032.
The yield on a 10-year treasury bond fell 0.25% to 1.61%.
The price of gold was up 1.36% to $1,740 per ounce.
Shares of Aliso Viejo-based chipmaker Microsemi Corp. was up about 4% to $19 and a market value of $1.7 billion. Semiconductors were generally up in midday trading Thursday.
Anaheim drug maker Questcor Pharmaceuticals Inc. rose about 3% to $28 for a market value of $1.7 billion.
Shares of Aliso Viejo-based QLogic Corp. rose about 4% to $9.50. The networking-equipment maker had a recent market value of $876 million.
Shares of Anaheim-based action-sports retailer Pacific Sunwear of California Inc. rose about 10% to $2, for a market value of $126 million. The company is expected to report third-quarter earnings after market close Thursday.