Chipmakers are in focus on Wall Street, with their shares turning mercurial this month and investors banking on a few dozen newly valuable companies to deliver nearly half of S&P 500 profit growth for the second quarter. The PHLX Semiconductor index has surged this year, reflecting massive gains at firms such as Micron Technology, Advanced Micro and Broadcom, but lately the 30-stock index has become a volatility show. The index is up 65% for the year, compared with a 9% gain in the S&P…
