I've never been blonde but I've had blondish highlights, and when I dyed it back, I used both permanent and semi-permanent dye on different occasions. I didn't really notice a huge difference in results to be honest. The first time I had a professional dye it back using permanent dye and the second, I just dyed it myself so I'm way too chicken to use semi-permanent on my own.

Make sure that you choose a shade that has a little red though. A lot of the time when people go from blonde to dark brown, their hair gets a green tint that looks really gross.