What is the ruling on the emission of semen resulting from frequent thoughts about sexual intercourse, and is this considered committing a major sin?

Deliberately thinking about intercourse, bringing it to mind, and deriving pleasure from it until semen is discharged is a prohibited act, requiring repentance. The Permanent Committee was asked about the ruling on a young, unmarried man thinking about intercourse, and it answered that it is impermissible because it is a means to indecency. However, if the thought is involuntary, there is no harm, as long as one does not intentionally dwell on the thought to seek pleasure and discharge semen, for this is not permissible.