Integra Resources (ITRG) had the highest return between 2019 and 2021 by a small-cap US stock, returning 537,400%.

ASSET	YEARS	% RETURN
Integra Resources (ITRG)	2019-2021	537,400%
Diversified Energy (DEC)	2019-2021	45,700%
Fubotv (FUBO)	2019-2021	8,668.36%
Digital Turbine (APPS)	2019-2021	3,196.76%
Fulgent Genetics (FLGT)	2019-2021	3,073.19%
Aspen Aerogels (ASPN)	2019-2021	2,237.56%
Lightwave Logic (LWLG)	2019-2021	1,966.67%
Atlanticus (ATLC)	2019-2021	1,892.18%
Aehr Test Systems (AEHR)	2019-2021	1,602.82%
A2Z Smart Technologies (AZ)	2019-2021	1,358%
Standard Lithium (SLI)	2019-2021	1,349.04%
HIVE Blockchain Technologies (HIVE)	2019-2021	1,253.85%
Celldex Therapeutics (CLDX)	2019-2021	1,188%
Kodiak Sciences (KOD)	2019-2021	1,100.85%
Anavex Life Sciences (AVXL)	2019-2021	1,071.62%
Xpel (XPEL)	2019-2021	1,023.03%
InMode (INMD)	2019-2021	945.63%
eXp World (EXPI)	2019-2021	858.75%
Perion Network (PERI)	2019-2021	828.57%
Lithium Argentina (LAR)	2019-2021	795.98%
Byrna Technologies (BYRN)	2019-2021	790%
Daqo New Energy Corp ADR (DQ)	2019-2021	776.14%
Clearfield (CLFD)	2019-2021	756.19%
IsoEnergy (ISOU)	2019-2021	740.46%
Microvision (MVIS)	2019-2021	735%

Small-cap stocks are treated as having a market cap between $300M and $2B.