This work investigates the anneal-induced positive charge in Hf-based dielectrics. It is found that anneal in forming gas produces substantially more positive charge than that in N-2 at 500 degrees C, indicating that hydrogen is a reactant for the positive charging. Positive charging is thermally accelerated and can occur in both HfO2 and Hf-silicates. Nitridation of either interfacial layer or whole dielectric stack enhances the positive charging significantly. These positive charges have a large sample-to-sample variation and are stable. For the first time, both mobile and fixed charges are simultaneously observed for Hf-stacks.