GameStop (GME) had the highest return in June 2013 by a large-cap US stock, returning 26.7%.

ASSET	MONTH	% RETURN
GameStop (GME)	June 2013	26.67%
Pilgrims Pride (PPC)	June 2013	24.71%
EXACT Sciences (EXAS)	June 2013	22.99%
Micron Technology (MU)	June 2013	22.06%
Sumitomo Mitsui Financial (SMFG)	June 2013	20.05%
EPAM Systems (EPAM)	June 2013	17.36%
Ciena (CIEN)	June 2013	15.65%
CoStar (CSGP)	June 2013	15.4%
Cboe Global Markets (CBOE)	June 2013	15.33%
Globus Medical (GMED)	June 2013	14.77%
T-Mobile US (TMUS)	June 2013	14.02%
Live Nation Entertainment (LYV)	June 2013	13.22%
Morningstar (MORN)	June 2013	12.84%
CME (CME)	June 2013	12.47%
Mizuho Financial (MFG)	June 2013	12.22%
Monster Beverage (MNST)	June 2013	11.76%
Western Midstream Partners (WES)	June 2013	11.54%
ServiceNow (NOW)	June 2013	10.54%
MakeMyTrip (MMYT)	June 2013	10.45%
Tesla (TSLA)	June 2013	9.98%
Webster Financial (WBS)	June 2013	9.88%
Charter Communications (CHTR)	June 2013	9.85%
Ulta Beauty (ULTA)	June 2013	9.73%
Mitsubishi UFJ Financial Group Inc ADR (MUFG)	June 2013	9.72%
America Movil SAB de CV ADR (AMX)	June 2013	9.24%

Large-cap stocks are treated as having a market cap of $10B+.