Determining the deposited energy of a gamma interaction in a scintillator is of vital importance for positron emission tomography (PET) imaging. In this article, a peak-based PET detector that simultaneously attains a high count rate is proposed. This detector exploits a known fact that a pulse peak is roughly linear with its energy. Therefore, a fast peak detector is designed for energy characterization using peaks directly acquired from scintillation pulses without any pulse shaping techniques. The key design of this peak detector is the utilization of comparators rather than amplifiers, along with a turbo-charged current source, so as to increase the slew rate and equivalently curtail the time it requires to catch the peak of a fast scintillation pulse in as few as around 40 ns. A PET detector prototype is implemented based on the designed circuit and experiments are carried out extensively to evaluate its performance. The prototype achieves an energy resolution of 14.8%@511 keV and a coincidence resolution time of 345 ps.