STPM or A Levels is recommended

But normally to study science stream in A Levels you will need a grade of B and above for the sciences...

And if you really consider to take the O Levels exam, please note that the syllabus is different and the way to answer the questions are harder than SPM. (I've got my hands on some O Levels exercise books in Popular, Ikano, they're a bit tough compared to SPM)

Just saying, in case you need to know.