In this paper, we introduce the notion of prime and semiprime ideal and characterize prime and semiprime ideals in a $\Gamma$-seminear-ring. Among them, for any $\Gamma$-seminear-ring, an ideal is semiprime if and only if it is the intersection of all primes containg it. Moreover, an ideal of a $\Gamma$-seminear-ring is prime if and only if it is semiprime and strongly irreducible.