  Let $R$ be a finite commutative ring with unity $1_R$ and $k \in R$.
Properties of one-sided $k$-orthogonal $n \times n$ matrices over $R$ are
presented. When $k$ is idempotent, these matrices form a semigroup structure.
Consequently new families of matrix semigroups over certain finite semi-local
rings are constructed. When $k=1_R$, the classical orthogonal group of degree
$n$ is obtained. It is proved that, if $R$ is a semi-local ring, then these
semigroups are isomorphic to a finite product of $k$-orthogonal semigroups over
fields. Finally, the antiorthogonal and self-orthogonal matrices that give rise
to leading-systematic self-dual or weakly self-dual linear codes are discussed.
