asp.net textbox value

I have 
<asp:TextBox Text="FirstName" ID="FNamefield"  runat="server" Height="22px" Width="253px"></asp:TextBox>  
and when i dont enter firstname value and click on submit , i get value in aspx.cs as Firstname  , but i should get as blank  , as the above is only to show user  , to enter firstname ..

or pls suggest how to show  as below