Vexillum semicostatum, common name the half-ribbed mitre, is a species of small sea snail, marine gastropod mollusk in the family Costellariidae, the ribbed miters.

[1] The shell size varies between 10 mm and 22 mm The shell is ovate.

The whorls of the spire are obtusely plicately ribbed.

The shell is chestnut-brown, the spire partially white.

[2] This species occurs in the Red Sea, the Indian Ocean off the Mascarene Basin, Madagascar and in the Pacific Ocean off Queensland, Australia and Papua New Guinea.