To get the Master Certification you need to pass:-
MOS: Microsoft Office Word 2010 Expert
MOS: Microsoft Office Excel 2010 Expert
MOS: Microsoft Office PowerPoint 2010
MOS: Microsoft Office Outlook 2010
or
MOS: Microsoft Office Access 2010
or
MOS: Microsoft SharePoint 2010
As you can see from the above (taken from Microsoft documentation) there isn't a separate exam for the Master Certification.
You need 4 passes to get the Master Certification.