The 17-year-old has caught the eye in the youth ranks of Hoffenheim and has appeared twice for their U-21 side also.
Born in Gambia, he travelled to Germany as a refugee at the age of 10, before joining Heidenheim and then Hoffenheim five years ago.
Sanyang is usually deployed as a winger and possesses great speed and dribbling ability, which would certainly match the playing style Bayern currently employ under Hansi Flick.
"Mamin is an extremely fast and dangerous winger. We see him as an ideal reinforcement for our Under-19 team and are very happy he will wear the Bayern jersey in the future," said academy manager Jochen Sauer.
Bayern have been on a bit of a youth recruitment drive recently, as in addition to Sanyang they have signed Armindo Sieb, also of Hoffenheim, centre-forward Lenn Jastremski from Wolfsburg and Luxemburgish striker David Jonathans from Swift Hesperange.