Should I address my GPA declination in my personal statement? Basically, my last two years GPA is much lower than my first two years: I got almost straight 4.0 in first two years but my junior year is a mess (one semester is 2.7) and my last semester GPA pump up a little with 3.5. I think the main reason is that I feel depressed with the over-packed schedule (I took 7 courses with a job in lab in the semester of 2.7) and slow progress of research. But, should I mention those in my personal statement?

I am triple majored in CS, Econ, and Math. I am planning to apply for Master degree in CS.

Thanks in advance.
Triple-majored and still above 3.5? That's very commendable. Typically when you refer to declines in academic perfomance, it's because your GPA is STILL low, perhaps below the minimum requirement for graduate school. But you seem to have graduated with an overall great GPA, and you should focus your personal statement instead on what you've learnt and done, such as research, projects, jobs - instead of that one year where things didn't go well. I'm sure you have a lot to talk about as it is.

EDIT: While a good GPA is necessary, your skill set and recommendations from your superiors you worked with are also as important. You need to show the school you're applying to what you can bring your field, which is what a personal statement is there for in the first place.