As you have asked about the ways to get jobs in Defence Research and Development Organization (DRDO) after B. Tech, I am giving you information about it, check below for the details

You can get the job in DRDO after B.Tech by following ways:

Recruitment Channel
Positions
Eligibility

Direct Entry through Scientist Entry Test (SET)
Class-I Officer Posts (Group A Service)

1st Class BE/ B.Tech in Chemical / Computer Science /Electrical/ Electronics &
Communication/ Mechanical Engineering

Campus Selection
Scientist 'B'

Final year/ Pre-final year student of BE/ BTech/BSc (Engineering)
Secured First Class or equivalent CGPA (with minimum 65% marks (7.25 CGPA)

Fellowships for instance: Aeronautical Research and Development Board Fellowship
Scientist ‘B’

BE/ BTech and ME/ MTech candidates of Aeronautical Engineering in the various institutes of national fame