What is a way to know my old semester marks from Anna University online?

From the release of the end-of-semester results until the deadline for applying for re-evaluation and photocopies of the answer sheets, students will have access to the online mark sheet. Check the email sent to your account that is connected to ACOE SEMS if you missed this. You receive a mark sheet in the mail that only includes the grade points—not the attendance rate or assessment scores. If for some reason, the mail wasn't delivered, you can request to see the mark sheet at the ACOE office or from your department's head, who enters the grades for the hard copy, if they are responsible for doing so. 

The only other choice is to wait until the end of the following semester when they distribute the hard copies if none of this passes muster. It is suggested that you check your marks within the allotted time and take a screenshot or save the pdf form to prevent such situations.