A semi-opera is a lyric Musical genre specifically English of the 17th century.

The London theaters were closed between 1642 and 1660 because of civil war. The rebirth of the theatrical activity was accompanied by a setting in music of the parts, initially in the form of Ballet S or in scenes of kind, without direct participation in the intrigue.

The semi-opera, particularly illustrated by Henry Purcell in his works Diocletian , King Arthur , The Fairy Queen , the Indian Queen , is an hybrid between the opera and the theater, and results from the increase in the musical participation: the priority is with the spoken drama, but of the sung vocal scenes appear and the music is used as entertainment there or its presence is justified by the intrigue and compatible with its progression.

The origin would be a will of realism, and that the English public could not have been satisfied of an entirely sung work. It is however this same public which, a few years later, was to be completely dedicated to the Italian opera: the semi-opera disappeared completely.