Diploma holders can not apply for colleges such as nits and IIITs through JEE mains. But there are many state level colleges, which offer Btech(lateral entry) to diploma holder students.Some of such university/colleges are-:

1-:COEP , Pune

• Eligibility-:Candidate must have completed Diploma Course in Engineering and Technology in relevant stream with minimum 45% marks  from an All India Council for Technical Education or Central or State Government approved Institution or its equivalent.

2-:VJTI , Mumbai

• Eligibility-:Candidate must have completed Diploma Course in Engineering and Technology in relevant stream with minimum 45% marks  from an All India Council for Technical Education or Central or State Government approved Institution or its equivalent.

3-:R.V. ENGINEERING COLLEGE and BMSCE, Bengaluru

• DCET 2020 is Diploma Common Entrance Test which is conducted by the Karnataka Examination Authority (KEA). The common DCET 2020 entrance test is a gateway for admissions to 2nd year undergraduate engineering programmes and 1st year undergraduate architecture programmes offered under the lateral entry scheme.

4-:Thapar Institute of engineering and technology,Patiala

• Eligibility-:diploma,    in    relevant    discipline,    of minimum    3-years    duration    after matriculation from  Polytechnic  College/Institute  affiliated  with  State  Board of   Technical   Education/University,   or   recognized   by   UGC/AICTE   with   a minimum  of  60%  marks  (55%  for  SC/ST)  in  aggregate  or  equivalent  grade point.

5-:Indraprastha University,Delhi

• Eligibility-:Candidate must have completed three-year diploma in relevant branches of Engineering/ Technology with a minimum of 60% marks in aggregate from any recognized Diploma awarding institute/ university/ board recognized by AICTE
• Admission-:Admission is through counselling based on the rank obtained in Guru Gobind Singh Indraprastha University Common Entrance Test (GGSIPU CET).

6-: AKTU(previously UPTU)-:

• Students after getting diploma must apply for upsee exam.

7-:LPU,Jalandhar

• Students can appear in LPUNEST after passing diploma.

8-:YMCA,Haryana

• Eligibility-:Candidate must have passed diploma in Engineering/Technology in relevant stream from a recognized University.
• Admission-:Admission is through HSTES (Haryana State Technical Education Society) counseling based on the rank obtained in LEET.

Hello Aspirant,

You can apply for JEE for engineering. However remember that you'll not be granted direct admission in 2nd year. You will get admission in 1st year in IITs, NITs and IIITs. However the private institutes offers admission in 2nd year for diploma holders.