The club's Under-20s player of the year in 2012 scored two tries on his Super League debut in their 34-22 win at Wakefield on Easter Monday, and scored a hat-trick in their 62-6 Challenge Cup win over North Wales last month.
Hull coach Peter Gentle said: "We have seen significant improvements in Jamie's game since he joined the first-team set-up and he is a young player that is developing well."
Shaul, who is currently playing on a dual registration with York, added: "Getting a one-year deal last year gave me something to work for and I'm over the moon to get a new one sorted."
