No Recognized Breed
There is no such thing as a “German Shepherd Chihuahua.” These are two completely different breeds with vastly different sizes, temperaments, and physical characteristics.
You might be thinking of a Chiweenie, a cross between a Chihuahua and a Dachshund. While a German Shepherd and Chihuahua could technically be bred, the offspring would simply be a mixed breed with no specific name.