Is int[] a reference type or a value type?

Arrays (even of value types like int) are reference types in C#.

http://msdn.microsoft.com/en-us/library/aa288453(VS.71).aspx:

In C#, arrays are actually objects. System.Array is the abstract base type of all array types.

The simplest test for reference type vs. value type is that reference types can be null, but value types can not.

Arrays are mechanisms that allow you to treat several items as a single collection. The Microsoft® .NET Common Language Runtime (CLR) supports single-dimensional arrays, multidimensional arrays, and jagged arrays (arrays of arrays). All array types are implicitly derived from System.Array, which itself is derived from System.Object. This means that all arrays are always reference types which are allocated on the managed heap, and your app's variable contains a reference to the array and not the array itself.

https://msdn.microsoft.com/en-us/library/bb985948.aspx