If you see all the Properties of Form in VB.NET, you will find
WindowState
Property.
Set this property value to
Maximized
your Form will be open with FullScreen Mode.
Or you can do the Same thing from Code. Write the Following Code on Form Load Event:
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.WindowState = FormWindowState.Maximized
End Sub
I hope it will help you. :)