Fellowship under KVPY SB stream is meant for students currently pusuing their first year Undergraduate programme in Basic Sciences.

The criteria for award of fellowship is as below:

"Students enrolled in the 1st year of undergraduate program in Basic Sciences namely Physics/Chemistry/Mathematics & Biology leading to B.Sc./B.S./B.Stat./B.Math./Int. M.Sc./Int. M.S. during the academic year 2017–18 and having secured a minimum of 60% (50% for SC/ST/PWD) marks in aggregate in MATHEMATICS and SCIENCE subjects (Physics/Chemistry/Biology)  in the XII Standard Board Examination. In the 1st year final examination of B.Sc./B.S./B.Math./B.Stat./Int. M.Sc./Int. M.S. they must secure 60% (50% for SC/ST/PWD) marks before taking up the fellowship, if awarded."

Hence you do not need an undergrad certificate but you need your Class XII marsksheet and 1st year Marksheet if you are shortlisted under SB stream.