美国生物博士要读几年？
PhD is 5 years. There are 4 semesters in the fall and spring and one in summer. Most students complete all degree requirements within 5 years， but some may need extra time to finish up thesis research. For instance， I was a part-time student and my PhD required six years of study. All course work had to be completed by the end of Spring Semester Year four. Thesis research will last an additional two to three years after that if you remain on track with your departmental goals/timeline.
Here's how it works... Fall & Spring Semesters： Two classes (9-13 weeks) are offered each semester for 300+ level courses. These would be your major core curriculum classes. You have to take these two classes every semester till you graduate（除非你延迟毕业或是休学） Otherwise， you can opt out and just do independent study or another course. To graduate， you must earn A or B in the above mentioned classes.
For most programs， it takes about ten months（除某些专业） to pass the course work phase with a passing grade. Then you move on to write your dissertation paper（有些专业需要先完成thesis proposal才能开始写dissertation，这个根据项目具体要求而定） You usually start thinking about your project/idea during your second year. After that， it depends on what type of project you choose to do. Some projects are more "data driven" while others are “conceptual” or “theoretical”. In general， if you stay committed to your studies， keep up with classwork， and stay engaged with your committee， you’ll be able to complete your degree in five(5)years. And that includes times when you might need to take a break to rest， recover，or even get married！