This way
HTML
<asp:TextBox ID="txtMessage" runat="server" TextMode="MultiLine" Rows="5" Columns="20" />
<br />
<br />
<hr />
<br />
<asp:Button ID="Button1" Text="Click To see same format Text" runat="server" OnClick="ShowMessage" />
<br />
<br />
<asp:Label ID="lblMessage" Text="" runat="server" />
VB.vb
Protected Sub ShowMessage(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
lblMessage.Text = txtMessage.Text.Replace(Environment.NewLine, "<br />")
End Sub
CS.cs
protected void ShowMessage(object sender, EventArgs e)
{
lblMessage.Text = txtMessage.Text.Replace(Environment.NewLine, "<br />");
}
Screenshot