ash's pikachu is not a boy

Ash's Pikachu is a male, you can see it from its tail and in season 16 Black and White there's a video where pikachu disguises as a female pikachu ^^

If you mean the voice actress is a girl, then yes....but many of the pokemon voices are done by girls...it is a male though, for it's tail does not have an m shaped tip.

Male

Um ya it is otherwise it would have a heart shaped tail instead of a lightning streak

In SS027 a female Pikachu is seen along with her trainer, Ayumi (Amy in English). A female Pikachu, like the one seen in SS027, has a heart shape at the end of her tail. This video is really cool, so go ahead and watch it if you want. I'm sure plenty of the American fans may want to know what an orginal Japanese episode of Pokemon is like, and don't worry the video has English subtitles.