To which type does a string in C# belong: reference or value?

The string type in C# is a reference type.

Although strings have some properties of value types (for example, behavior during comparison), their storage and management in memory are handled as for reference types. Declaring a variable of type string allocates memory on the stack for storing the reference, while the string itself is stored in the managed heap.

A key property of reference types is the ability to have a null value, which is also true for strings.

String immutability (unchangeability after creation) is a feature of the implementation and does not change their fundamental nature as reference types.