The German army entered the WWII whitout having any semi-automatic rifles (At this time there was already a few models in service on the Allied side.). When Germany attacked the USSR and met the soviet semi-auto rifles (Like the SVT-40, which also had a scoped version.), and suffered heavy casulties, they realized the need for such weapons. Later they started a contest for a rifle with a 10 round magazine. The Walther and Mauser factory made their own versions for the contest. The Walther G-41 won the competition, which has many similiraties with the SVT-40. Later the improved version of it started it's service as the G-43.
G-43 (Gewerh 43) on Wikipedia