Semester breaks are generally not so long. Hardly it would be of 1-2 weeks. But there are certain number of holidays in the year which one would be getting. 

There is nothing called as a midsem week in IITM,let alone midsemester holidays.

There are only holidays for festivals and nothing else.Dont get disappointed though,semester holidays are really long.

Below is the link to the calendar for the upcoming semester.