A year ago I completed a history unit at university on the Holocaust, and while looking extermination camps it was deemed that there were six: Chełmno, Bełżec, Sobibór, Treblinka, Auschwitz-Birkenau and Majdanek. However, a recent glance at the Wikipedia article on death camps reveals an extra camp called Maly Trostenets. Is Maly Trostenets rightly included?
The camps of Sajmište and Jasenovac are also not included from on list but are documented extermination camps. I'm unsure why they, along with Maly Trostenets, were not included on that list.
It may have been an oversight, or may have been a practical constraint of time/focus. Wikipedia has articles on each and categorizes all three as extermination camps if you want a brief overview or to pursue their primary sources.