Use MemoryStream with StreamWriter and StreamReader : MemoryStream « Stream File « VB.Net Tutorial

1. VB.Net Tutorial
2. Stream File
3. MemoryStream

Imports System.IO

public class Test
   public Shared Sub Main
        Dim memory_stream As New MemoryStream()
        Dim stream_writer As New StreamWriter(memory_stream)
        stream_writer.Write("aaa.")
        stream_writer.Flush()

        Dim stream_reader As New StreamReader(memory_stream)
        memory_stream.Seek(0, SeekOrigin.Begin)
        Console.WriteLine(stream_reader.ReadToEnd())
        stream_reader.Close()

   End Sub
End class

aaa.