I have done a Bachelor's (4 years) and my GPA is quite low. But I have research experiences (more than 3 years) and few publications in some good journals. I want to do a Ph.D. in biology or a related field. Is it possible to get a position (e.g. in the USA or Europe) when research experience is the only strong point? Or should I go for a Master's first?
In the UK a PhD (or DPhil) typically starts after a 4-year undergrad program: so yes, it's normal to do a PhD right after your undergrad.
At a top-level research institution in the USA (at least in the sciences, and biology is what you said you want to pursue) a Masters is something that you would normally only get if you dropped out of a PhD program: so yes it's normal to do a PhD right after your undergrad.
In Canada, for some reason the majority of the people think they have to do a Masters before a PhD, but there is no university in Canada that requires a Masters to do a PhD in biology. In fact NSERC funding for your PhD will last only 3 years if you have a Masters, and 4 years if you do not: so yes, there is a way for you to start your PhD right after your undergrad.
People have mentioned that it's normal in Denmark and Australia too.
Some European universities (for example some, but not all, universities in Germany) you might require a Masters.
Now for some advice:
But I have research experiences (more than 3 years) and few publications in some good journals. I want to do a Ph.D. in biology or a related field. ... should I go for a Master's first?
You have more publication experience than some people have after their first post-doctoral position. A "few publications in some good journals" is what PhD students aim towards for graduation.
Masters programs can take 1 to 3 years (longer if your experiments don't work out). Why not instead do a 3-year PhD program in UK or most of Europe, or a 4-year "direct" PhD program in USA or Canada, and get Doctor beside your name for the rest of your life?
If you're going to do research for the next 6 years, would you rather:
- Earn a Masters salary (e.g. ~$25,000/year in Canada) for 2 years, then a PhD salary (e.g. ~$35,000/year in Canada) for 4 years, or
- Earn a PhD salary (e.g. ~$35,000/year in Canada) for 3-4 years, then a post-doc salary (e.g. $40,000-$70,000/year in Canada) for the remaining 2-3 years?
These days, it is getting harder and harder to get a stable job while our bodies are still in their prime condition for raising a family (or doing whatever else we enjoy). There still are PhDs getting permanent or tenure-track jobs in their 20s, but it's becoming common for people to reach 40 by the time this happens, because there's more humans to compete with than any time in our history. Do you really want to delay your life by 2-3 years by getting a Masters, when your goal is to get a PHD?
I am of course not listing the advantages of doing a Masters rather than a PhD, since you said you want to do a PhD eventually, and you seem to be a very strong candidate for a PhD position, so with no other information, I am certainly happy to encourage you to go straight to a PhD position. If you do want to know the reasons why one would choose a Masters rather than a PhD, the reasons do exist, but to explain them might double the size of this answer, and I would only do it if there was some reason why you were still considering a Masters even though you now know that it's not abnormal to go straight to a PhD: perhaps in that case you could describe what you want and the reasons for it, in a separate question).
It's certainly possible -- in fact, in the USA it's more common to start a PhD directly after a Bachelor's than after a Master's. In Europe, having a Master's first is a more typical requirement, but I have known some people to start PhDs straight after their Bachelor's (in physics, in the UK). Having significant research experience and published papers will certainly help your application a lot.
Why not apply for PhD and Master's positions at the same time? That way, you may get accepted to a PhD, in which case great, if not then you will likely have the Master's to fall back on.
In Denmark, at least at the University of Copenhagen, they have a 3+5 and 4+4 PhD programs:
In the 3+5 system, you start on an integrated Masters and PhD process straight after graduating with your Bachelors.
It exists at the Aarhus University as well, see section "I'm doing/have a Bachelor's degree". The other Danish universities may have something similar, you can google.
Some programs that don't accept people without a master's degree into their PhD program have a "bypass" mechanism where you can essentially decide after completing the first part of your program that you want to treat your completed work as the first part of your PhD program rather than completing the requirements for the Master's degree. (For example, here's the description from the University of Alberta nursing programme.) You usually need to have performed up to some standard and have the agreement of your supervisor, but the requirements are generally not onerous. (This web page says this is a Canadian thing; it existed at my previous institution (a top research university in the US) when I was there 15 years ago, but seems to have disappeared since then.)
I have done exactly that, I had a Bachelor from Switzerland and did a PhD in the UK. I think it is more common in the US than in Europe. In Europe you might be more successful in getting a PhD position in a field where your research experience is relevant. I ended up with a PhD position in a group I had previously collaborated with. They had to invest a lot less time into my training and I got a PhD out of it, so it worked out for everyone.