4.1.1 The System.ValueType type
Visual Studio .NET 2003
All value types implicitly inherit from the class System.ValueType, which, in turn, inherits from class object. It is not possible for any type to derive from a value type, and value types are thus implicitly sealed (Section 10.1.1.2).
Note that System.ValueType is not itself a value-type. Rather, it is a class-type from which all value-types are automatically derived.