The author of this very article does not think so. Here is the book that he wrote:
But, was Mohammad a historical person?
Muhammad Sven Kalisch is an Islamic researcher at the University of Münster. He is also the first person in Germany to hold a Chair of Islamic Religion. Kalisch’s recent public admission that he is unsure whether the Prophet Muhammad was actually a historical person has got him into hot water.
http://www.freerepublic.com/focus/f-news/2088564/posts
Later he remove Muhammad from his name, i.e. it is now only Sven Kalisch https://wikiislam.net/wiki/Sven_Kalisch