There are number of colleges in US which provide a top notch PhD program in Biotechnology, including:

1. University of California, San Diego

2. University of California, San Francisco

3. Pennsylvania State University

4. University of Washington

5. Johns Hopkins University

Most of these universities require GRE scores as one of the prerequisites for admission. Earning a GRE score of 325+ (where quantitative score is 165+ out of 170) generally ensures that a candidate is applicable to apply for all top notch colleges and universities.

In addition, most of the best colleges require 100+ score in the TOEFL iBT english proficiency test. Within this, for prospective PhD students, a speaking score of 25+ out of 30 is generally preferred.