Let n1, n2,. .. , n d be positive integers and H be the numerical semigroup generated by n1, n2,. .. , n d. Let A := k[H] := k[t n 1 , t n 2 ,. .. , t n d ] ∼ = k[x1, x2,. .. , x d ]/I be the numerical semigroup ring of H over k. In this paper we give a condition (*) that implies that the minimal number of generators of the defining ideal I is bounded explicitly by its type. As a consequence for semigroups with d = 4 satisfying the condition (*) we have µ(in(I)) ≤ 2(t(H)) + 1 .