I worked at company A this past summer as a PhD intern (the position only required the candidate to be pursuing a Bachelor’s degree) where about half of my responsibility was directly related to machine learning. Overall, the experience went very well and they offered me the opportunity to continue working for them part time during the semester while I was away at school; it was implied that this could lead to further employment in the form of an internship or full time position in the future, but it was never formally stated or agreed upon.

Fast forward to now: Companies B, C, and D are contacting me with further internship opportunities. These companies would likely look better on a CV (or at least offer my CV a larger diversity of experience), and put me in roles that appear to align more closely with my career goals; I’m also not crazy about the industry of company A.

My Question: Is it unethical for me to accept a position with company B, C, or D this summer? I think it’s better for me as a researcher to get a diversity of experience by joining a new company, and the roles could teach me things I won’t learn by going back to company A a second time. That being said, I’m not ruling out company A as a possible landing location when I get a full time position after graduation; I don’t want to burn any bridges.