Umm, no.... Most large studios don't do development in C#(CSharp)
I've never programmed in C#, but I've heard that the automated garbage collector causes a sharp hit in performance. I have seen a 3D engine programmed in C#, but it was pretty crude.
However, a google check did show an engine called Axiom, which is a C# port of OGRE, which is a decent opensource engine, so who knows, maybe...