This study investigates the response of Timepix3 semiconductor pixel detectors in proton beams of varying intensities, with a focus on FLASH proton therapy. Using the Timepix3 application-specific integrated circuit (ASIC) chip, we measured the spatial and spectral characteristics of 220 MeV proton beams delivered in short pulses. The experimental setup involved Minipix readout electronics integrated with a Timepix3 chipboard in a flexible architecture, and an Advapix Timepix3 with a silicon sensor. Measurements were carried out with Timepix3 detectors equipped with experimental gallium arsenide (GaAs) and silicon (Si) sensors. We also investigated the response of a bare Timepix3 ASIC chip (without sensor). The detectors were placed within a waterproof holder attached to the positioning system of the IBA Blue water phantom, with additional measurements performed in air behind a 2 cm-thick polymethyl methacrylate (PMMA) phantom. The results demonstrated the capability of the Timepix3 detectors to measure time-over-threshold (ToT, deposited energy) and event counts (number of events in a pixel) in both conventional and ultra-high-dose-rates (UHDR) proton beams. The bare ASIC chip configuration sustained up to a dose rate (DR) of 270 Gy/s, the maximum tested intensity, although it exhibited limited spatial resolution due to low detection efficiency. In contrast, Minipix Timepix3 with experimental GaAs sensors showed saturation at low DR∼5 Gy/s. Furthermore, the Advapix Timepix3 detector was used in both standard and customized configurations. In the standard configuration (Ikrum = 5), the detector showed saturation at DR∼5 Gy/s. But, in the customized configuration when the per-pixel discharging signal (called “Ikrum”) was increased (Ikrum = 80), the detector demonstrated enhanced performance by reducing the duration of the ToT signal, allowing beam spot imaging up to DR=∼28 Gy/s in the plateau region of the Bragg curve. For such DR or higher, the frame acquisition time was reduced to the order of microseconds, meaning only a fraction of the pulse (with pulse lengths on the order of milliseconds) was captured.