The court described the incident as "rarest of rare" and sent Rishi to the gallows for the January 24 incident.
According to police chargesheet, Rishi first raped the victim and then killed her in a village in Katihar.
Police officials said that it was the first time that any court in Bihar had awarded death to a rapist in a record time of nine days after the shocking December 16, 2012 gangrape of a student in Delhi that triggered protests across the country.