Semenyih is a town and a mukim in Hulu Langat District in southeastern Selangor, Malaysia along the Kajang–Seremban road.

[citation needed] A 1.5 billion ringgit incinerator project was planned for a site between Semenyih and nearby Broga by the federal government.

In early 2005, a temporary injunction was issued, stopping work on the project, in response to a lawsuit by residents of the two towns.

Highway 31, traversing the Langat valley, starts here and connects to Bangi, Putrajaya (precinct 20), Dengkil and Banting.

Semenyih is served by the UNMC-Kajang Shuttle Bus, going from University of Nottingham's campus near Broga to  KG35  KB6  Kajang MRT/railway station.