List gets null while it should not be?

Question

I have the following class:

 public class MyClass
    {
        private List<Queue> listOfItems;
        private int someInteger;

        public MyClass()
        {
            List<Queue> listOfItems = new List<Queue>();
            listOfItems.Add(new Queue()); // THIS WORKS
            someInteger = 0; // THIS WORKS
        }

        public void SetValue()
        {
            someInteger = 1; // THIS WORKS
            listOfItems.Add(new Queue()); // THIS FAILS, WHY?!?
        }

    }

I use the following:

MyClass test = new MyClass();
test.SetValue();

This generates the following error at the underlined line of the class code: System.NullReferenceException: Object reference not set to an instance of an object.

Why is that and how to fix it? Thanks for any reply!