Hydrogenation of metal/thin oxide/p-type silicon and metal/n-type silicon diodes has been studied using high frequency capacitance profiling. In situ observations of acceptor and donor passivation were made while H ions were implanted through thin gate metallizations. Direct measurement of ion transits at a variety of electric fields establish that a unique mobility can be assigned to positive H ions, and modeling of low and high field data in both n and p-type samples is consistent with the notion that the positive charge state is occupied ~1/10 of the time. The time dependence of hydrogen penetration for both p and n-type diodes indicates that hydrogen is, in addition to being trapped at unpassivated shallow donors or acceptors, becoming immobilized at other sites in silicon. The density of these secondary trapping sites correlates well with the shallow dopant population suggesting that additional hydrogen atoms may become trapped near already-passivated dopant atoms.