It's possible you might be thinking of a Chiweenie, which is a cross between a Chihuahua and a Dachshund.
While you can certainly breed a German Shepherd with a Chihuahua, the offspring would be a mixed breed with no specific name.
Is there such thing as a German Shepherd chiuahua?
No, there is no such thing as a "German Shepherd Chihuahua". These are two completely different breeds with vastly different sizes, temperaments, and physical characteristics.