NEW YORK — US stocks are starting the second half of 2013 on a positive note after the market closed out its best first half of a year in more than a decade.

The Dow Jones industrial average was up 100 points, or 0.7 percent, at 15,009 after the first few minutes of trading Monday. All but one of the 30 stocks in the index rose.

The Standard & Poor's 500 index was up 11 points, or 0.7 percent, at 1,617. The S&P 500 had its best first half of a year since 1998, returning 13.8 percent with dividends reinvested.

The Nasdaq composite was up 32 points, or 1 percent, at 3,435.

Onyx Pharmaceuticals jumped 51 percent to $131 on news that the company received an unsolicited takeover bid from Amgen.