Onalaska High School is a public high school in Onalaska, Wisconsin, in the Onalaska School District. It had an enrollment of 933 students in grades 9-12 for the 2022-23 school year.

The first public high school in Onalaska was founded in January 1890 on a plot of land between Main, King, Fourth and Fifth Streets. The first graduating class had three students, and the school was known as the Vikings, with the school colors being red and white. The original building burned down in 1895, and a new building was built on-site the following year. After another fire in 1924 left the new building completely destroyed, all students in the Onalaska public school system moved to the former La Crosse County School of Agriculture. The school's colors changed to purple and white in the 1940s, and the "Hilltopper" moniker came soon after that due to the location of the school, dubbed "Heaven on a Hill". Another new building was built due to growing student counts in 1970.

Onalaska offers Advanced Placement classes. About half of all seniors take AP classes.

OHS is 71.7% white, 12.6% Asian, 6.1% Hispanic, 6.1% two or more races, 2.4% black, and 0.4% American Indian, and 0.1% Native Hawaiian/Pacific Islander. OHS is 48% female and 52% male.

The Hilltoppers boys' basketball team has won three WIAA championships: the Class A championship in 1988, the Class B championship in 1992, and the Division 2 championship in 2012.

Additionally, OHS has won state titles in the following sports:

• Boys' Cross Country: 2021
• Boys' Golf: 1982, 1985
• Girls' Golf: 1989
• Girls' Gymnastics: 1985, 1997, 1998

OHS has two competitive show choirs, the higher-level Hilltoppers and lower-level Express. The Hilltoppers have been a top show choir in the nation for three decades, winning a competition in Wisconsin Dells, Wisconsin in 1984. From 1985 - 2006, led by Paul Gulsvig, the Hilltoppers competed in 140 competitions, won grand championships in 16 cities and 7 states, won national championships in 2004 and 2006, and made the finals in all but two of the competitions in the 21-year period.

They continue to be a major force, ranking 2nd in the nation, winning six grand championships, best band, and best vocals awards in their 2020 season with their show themed after the Netflix TV series The Umbrella Academy. OHS also hosts its own annual competition, the Onalaska Show Choir Classic, which started in 1987. It is noted for being one of the toughest competitions in the Midwest and attracts schools from Wisconsin, Minnesota and Iowa.

• Tim Gullikson, professional tennis player and coach
• Tom Gullikson, professional tennis player and coach
• Chuck Hockenbery, professional baseball player
• Michael Huebsch, Wisconsin politician
• Sandra Lee, professional chef and television personality
• Tom Newberry, professional football player
• Frank Pooler, composer
• Mark Proksch, comedian and actor
• Matt Thomas, basketball player for the Utah Jazz
• Jack Olsen, Grounded Man Of The Year

• Onalaska High School