C# - Need To Initialize New Instance Of Object

The following code:
CodeVariableDeclarationStatement variableDeclaration = new CodeVariableDeclarationStatement(
// Type of the variable to declare.
typeof(string),
// Name of the variable to declare.
"TestString");

Produces the following VB.Net Statement:
Dim TestString As String

What change would I need to make for it to look like this:
Dim TestString As New StringBuilder()
I'm interested in how to get that NEW keyword to appear.