Taiwan Semiconductor Manufacturing (TSM) had the highest return in March 2014 by a mega-cap US stock, returning 12.1%.

ASSET	MONTH	% RETURN
Taiwan Semiconductor Manufacturing (TSM)	March 2014	12.09%
ASML Holding NV ADR (ASML)	March 2014	9.82%
Advanced Micro Devices (AMD)	March 2014	9.56%
Applied Materials (AMAT)	March 2014	9.2%
Seagate Technology (STX)	March 2014	8.52%
Banco Santander SA ADR (SAN)	March 2014	8.13%
Microsoft (MSFT)	March 2014	8.1%
Wells Fargo (WFC)	March 2014	7.87%
JPMorgan Chase (JPM)	March 2014	7.83%
Johnson & Johnson (JNJ)	March 2014	7.79%
Berkshire Hathaway (BRK.A)	March 2014	7.61%
Berkshire Hathaway (BRK.B)	March 2014	7.59%
UnitedHealth (UNH)	March 2014	7.28%
KLA (KLAC)	March 2014	7.26%
Lam Research (LRCX)	March 2014	7.15%
Broadcom (AVGO)	March 2014	5.78%
Oracle (ORCL)	March 2014	5.66%
Bank of America (BAC)	March 2014	5.58%
Texas Instruments (TXN)	March 2014	5.55%
Intel (INTC)	March 2014	5.15%
International Business Machines (IBM)	March 2014	5%
Marvell Technology (MRVL)	March 2014	4.78%
Cisco Systems (CSCO)	March 2014	3.94%
Chevron (CVX)	March 2014	3.59%
Novartis AG ADR (NVS)	March 2014	3.57%

Mega-cap stocks are treated as having a market cap of $200B+.