Article VI of the US Constitution says that the Constitution is the a. Supreme Law of the Land.
It is written in the clause 2 of the article mentioned, which is also known as the "Supremacy Clause". The clause establishes the Constitution as the Supreme Law of the Land and therefore all states, federal officers and judges are bound by it, meaning that in case of a conflict between state and federal laws, the federal laws is the one that shall prevail.