Silicon Motion Technology (SIMO) had the highest return between 2010 and 2011 by a mid-cap US stock, returning 495.4%.

ASSET	YEARS	% RETURN
Silicon Motion Technology (SIMO)	2010-2011	495.36%
Astronics (ATRO)	2010-2011	314.94%
Golar LNG (GLNG)	2010-2011	313.75%
First Majestic Silver (AG)	2010-2011	312.74%
Novanta (NOVT)	2010-2011	301.18%
PriceSmart (PSMT)	2010-2011	250.7%
Chart Industries (GTLS)	2010-2011	221.65%
Sirius XM (SIRI)	2010-2011	198.36%
Universal Display (OLED)	2010-2011	191.89%
Melco Resorts & Entertainment (MLCO)	2010-2011	177.24%
Lithia Motors (LAD)	2010-2011	172.59%
Fortuna Silver Mines (FSM)	2010-2011	167.54%
New Gold (NGD)	2010-2011	167.37%
Bath & Body Works (BBWI)	2010-2011	167.25%
Polaris Industries (PII)	2010-2011	166.01%
CVR Energy (CVI)	2010-2011	163.81%
Under Armour Inc A (UAA)	2010-2011	161.34%
B2Gold (BTG)	2010-2011	161.02%
Crocs (CROX)	2010-2011	151.62%
Endeavour Silver (EXK)	2010-2011	149.62%
DXP Enterprises (DXPE)	2010-2011	142.84%
Dillard's (DDS)	2010-2011	141.83%
Dorman Products (DORM)	2010-2011	132.41%
Boston Beer (SAM)	2010-2011	130.39%
Cirrus Logic (CRUS)	2010-2011	130.04%

Mid-cap stocks are treated as having a market cap between $2B and $10B.