To make a winform fullscreen in C# and VB.NET you can use the following snippet.

Sample C#

public void SetFormFullscreen()
{
	this.TopMost = true;
	this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
	this.WindowState = System.Windows.Forms.FormWindowState.Maximized;
}

Sample VB.NET

Public Sub SetFormFullscreen()
	Me.TopMost = True
	Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None
	Me.WindowState = System.Windows.Forms.FormWindowState.Maximized
End Sub