Arm Holdings plc American Depositary Shares (ARM) had the best day in Q3 2023 by a mega-cap US stock on September 14, 2023, returning 13.4%.

ASSET	DATE	% RETURN
Arm Holdings plc American Depositary Shares (ARM)	9/14/2023	13.35%
NVIDIA (NVDA)	8/14/2023	8.07%
Tesla (TSLA)	8/29/2023	7.8%
Arm Holdings plc American Depositary Shares (ARM)	9/25/2023	6.49%
Dell Technologies (DELL)	9/1/2023	6.4%
Micron Technology (MU)	8/14/2023	6.07%
Palantir Technologies (PLTR)	7/10/2023	6.05%
Palantir Technologies (PLTR)	7/17/2023	5.97%
Caterpillar (CAT)	8/1/2023	5.83%
Crowdstrike (CRWD)	8/31/2023	5.79%
Palantir Technologies (PLTR)	8/30/2023	5.63%
NVIDIA (NVDA)	8/21/2023	5.56%
Palantir Technologies (PLTR)	8/23/2023	5.52%
Palantir Technologies (PLTR)	8/29/2023	5.48%
Palantir Technologies (PLTR)	7/31/2023	5.42%
Netflix (NFLX)	7/18/2023	5.28%
Analog Devices (ADI)	8/23/2023	5.26%
Marvell Technology (MRVL)	8/14/2023	5.23%
Tesla (TSLA)	7/24/2023	5.16%
Morgan Stanley (MS)	7/18/2023	5.03%
Advanced Micro Devices (AMD)	9/28/2023	4.92%
Advanced Micro Devices (AMD)	8/14/2023	4.9%
Tesla (TSLA)	9/5/2023	4.69%
Alibaba (BABA)	7/24/2023	4.65%
Dell Technologies (DELL)	8/8/2023	4.61%

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