Consider a multiplicative group of integers modulo $n$, denoted by $mathbb{Z}_n^*$. Any element $a{in}mathbb{Z}_n^*$ is said to be a semi-primitive root if the order of $a$ modulo $n$ is ${phi}(n)/2$, where ${phi}(n)$ is the Euler phi-function. In this paper, we discuss some interesting properties of the multiplicative groups of integers possessing semi-primitive roots and give its applications to solving certain congruences.