- semisimple class
- semisimple element
- semisimple group
- Semisimple Jordan algebra
- semi-simple Lie algebra
- semi-simple Lie group
- semisimple matrix
- semi-simple module
- semi-simple of BCI-algebras
- semisimple ring
- semisimple semiring
- semi-simple transformation
- semisimplicity theorem of group algebra
- semi-space
- semi-space
- semi-sphere
- semi-spherical surface
- semi-stability
- semi-stable limit cycle
- semi-stratifiable space
- semi-term
- semi-thinness
- Semi-Thue grammar
- semi-Thue system
- semi-valuation with extensionality