By Rex Crum, MarketWatch

SAN FRANCISCO (MarketWatch) -- Tech stocks were rising Tuesday, with Apple Inc. among the sector leaders as speculation begins to grow about what the company has planned for the next version of the iPhone.

Apple (AAPL) was up by 61 cents a share, at $91.46, following reports that said the company is set to begin production of the so-called iPhone 6 in China next month. The newest version of Apple's smartphone will reportedly come out in two models, with screen sizes of 4.7 inches and 5.5 inches, and will ship in September. If such reports end up being true, the next release would fall in line with Apple's historical pattern of introducing a new iPhone in time for the annual Christmas and holiday shopping seasons.

If Apple does increase the size of its iPhone screens, it would add to the arms race that has developed around bigger screens for smartphones. Apple rivals such as Samsung and HTC have released phones with screens of up to 5.7 inches, and last week, Amazon.com Inc. (AMZN) unveiled its Fire phone with a 4.7-inch screen.

Groupon (GRPN) added to its prior-day's gains by rising more than 9% to $7.08 a share. On Monday, Piper Jaffray analyst Gene Munster said recent checks show Groupon has increased the number of deals available on its site, and is taking more steps in its turnaround to become more of a destination for e-commerce consumers.

Munster said Groupon has increased the number of deals on its network to 200,000 from about 140,000 at the end of 2013, and he expects the company to reach 500,000 deals within three to four years.

Micron Technology Inc. (MU) rose 4.5% to $32.67 a share after the memory chipmaker reported better-than-expected quarterly results late Monday.

Online radio company Pandora Media Inc. (P) was up by 4% at $29.32 a share. Canaccord Genuity analyst Michael Graham said that recent meetings with Pandora have given him "renewed confidence in Pandora's ability to exceed our revenue targets over time."

The tech-heavy Nasdaq Composite Index (RIXF) climbed by 28 points to 4,396 and the Philadelphia Semiconductor Index (SOX) rose 0.5%.

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