In this paper, we study half lightlike submanifolds M of an indefinite generalized Sasakian space form M̄(f1, f2, f3), with an indefinite trans-Sasakian structure of type (α, β), subject to the condition that the structure vector field of M̄ is tangent to M . Our main result is a characterization theorem for such a half lightlike submanifold. Mathematics Subject Classification: 53C25, 53C40, 53C50