Holacanthus semifasciatus Kamohara, 1934 Genicanthus semifasciatus, the Japanese swallow, is a species of marine ray-finned fish, a marine angelfish, belonging to the family Pomacanthidae.

Genicanthus semifasciatus is sexually dichromatic; the males and females show different colouration and patterning.

The dorsal area of females is greyish brown and white ventrally, with a yellow margin to the dorsal fin with a black head and caudal fin, and black on the head and tail.

This species is protogynously hermaphroditic and is normally encountered in harems consisting of a male and several females.

[3] Genicanthus semifasciatus was first formally described in 1934 as Holocanthus semifasciatus by the Japanese ichthyologist Toshiji Kamohara (1901–1972) with the type locality given as Kashiwajima in the Kochi Prefecture of Japan.