Gilead Sciences (GILD) had the highest return between 1995 and 2004 by a mega-cap US stock, returning 2,845.2%.

ASSET	YEARS	% RETURN
Gilead Sciences (GILD)	1995-2004	2,845.19%
Amazon (AMZN)	1995-2004	1,716.65%
Citigroup (C)	1995-2004	1,036.64%
Cisco Systems (CSCO)	1995-2004	893.65%
Amgen (AMGN)	1995-2004	771.67%
ASML Holding NV New York Registry Shares (ASML)	1995-2004	749.08%
UnitedHealth (UNH)	1995-2004	686.46%
Microsoft (MSFT)	1995-2004	683.92%
RTX (RTX)	1995-2004	681.76%
Morgan Stanley (MS)	1995-2004	664.03%
Costco Wholesale (COST)	1995-2004	657.42%
Wells Fargo (WFC)	1995-2004	593.51%
Toronto Dominion Bank (TD)	1995-2004	572.51%
Applied Materials (AMAT)	1995-2004	555.34%
American Express (AXP)	1995-2004	542.28%
Analog Devices (ADI)	1995-2004	536.83%
Oracle (ORCL)	1995-2004	529.65%
Royal Bank of Canada (RY)	1995-2004	509.84%
Bank of America (BAC)	1995-2004	505.12%
Intel (INTC)	1995-2004	504.29%
International Business Machines (IBM)	1995-2004	478.19%
Texas Instruments (TXN)	1995-2004	453.61%
Johnson & Johnson (JNJ)	1995-2004	439.65%
Walmart (WMT)	1995-2004	427.5%
GE Aerospace (GE)	1995-2004	425.05%

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