Here you will find USABO semifinal exam past papers.
USABO Semifinal exam 2003 Answer Key
USABO Semifinal exam 2004 Answer Key
USABO Semifinal exam 2005 Answer Key
USABO Semifinal exam 2006 Answer Key
USABO Semifinal exam 2007 Answer Key
USABO Semifinal exam 2008 Answer Key
USABO Semifinal exam 2009 Answer Key
USABO Semifinal exam 2010 Answer Key
USABO Semifinal exam 2011 Answer Key
USABO Semifinal exam 2012 Answer Key
For new papers please register.
Source: https://www.usabo-trc.org/