  In this article, we study skew constacyclic codes over a class of finite
commutative semisimple rings. The automorphism group of
$\mathcal{R}=\prod_{i=1}^t F_q$ is determined, and we characterize skew
constacyclic codes over ring by linear codes over finite field. We also define
homomorphisms which map linear codes over $\mathcal{R}$ to matrix product codes
over $F_q,$ some optimal linear codes over finite fields are obtained.
