He has been sidelined for the rest of the season after suffering a knee injury in training which required surgery.
"I am very happy that Gabi has signed a new contract with us," manager Mikel Arteta told the club website https://www.arsenal.com/news/martinelli-signs-new-long-term-contract. "He is a very talented young player and he has impressed us with his performances, attitude and work-rate.
"We are looking forward to getting him back to full fitness and to watching his development at our club."
Martinelli is the first teenager to score 10 goals in a season for Arsenal since Nicolas Anelka over 20 years ago. (Writing by Ken Ferris; Editing by Pritha Sarkar)