For M. Tech. , one needs to have a B.Tech degree or BE degree as technical knowledge is required. For BSc students, they first need to study MSc or MCA and then apply for M.Tech. You can check the websites of the college you want to apply to so as to find their minimum requirements

Hello dear aspirant, 

You can't pursue M. Tech after a B.Sc degree,  you have to pursue M.Sc after B.Sc and only after completing M.Sc,  you can appear in GATE and pursue M. Sc. 

Hope I am clear.