Help with Replace method - Replace only the exact text

Hi,
I am using C# and ASP.NET 4.0 and using a web application.
I have a string which contains "MainId;IsMainIdRequired;MainText;MainNote"
I am trying to do a replace method like the below:
strOriginalOrder = strOriginalOrder.Replace("MainId", ""); I need to replace only the exact text, but the above is also replacing the text of IsMainIdRequired.
How to only replace the exact text?
Thanks