US STOCKS-Mid- and small-caps rise, outperform S&P 500

By Caroline Valetkevitch

NEW YORK, Sept 11 (Reuters) - Small- and mid-cap shares were outperforming the major U.S. stocks indexes on Thursday, boosted by shares of JDS Uniphase Corp and GT Advanced Technologies Inc.

S&P MidCap 400 index was up 0.4 percent while the S&P SmallCap 600 index was up 0.7 percent. The benchmark S&P 500, by comparison, was down 0.1 percent.

JDS Uniphase shares were up 10.2 percent, giving the mid-cap index its biggest boost. Late Wednesday, it said it would split into two public companies as it looks to expand in data communication market and strengthen its network business. RBC Capital Markets raised its rating on the stock.

Shares (Frankfurt: DI6.F - news) of GT Advanced Technologies (Xetra: A1JDP0 - news) were up 6.9 percent, rebounding after losing roughly 26 percent in the previous two sessions. The losses followed news Apple Inc (NasdaqGS: AAPL - news) 's new large-screen iPhones would not have GT's sapphire screens.

The MidCap index is up 6.9 percent for the year so far while the SmallCap index is down 0.3 percent, but below the S&P 500's 8 percent gain since Dec. 31.

Index snapshot at 15:23 EDT:

* S&P 500 was falling 0.05 points, or -0 percent.

* Nasdaq Comp was losing 0.65 points, or 0.01 percent.

* Dow industrials was dropping 30.41 points, or 0.18 percent.

* Russell 2000 was adding 7.26 points, or 0.62 percent.

* S&P MidCap was adding 5.13 points, or 0.36 percent.

* S&P SmallCap was gaining 4.58 points, or 0.69 percent. (Editing by Bernadette Baum and Nick Zieminski; Editing by Lisa Shumaker)