This study explores sub-cycle control of terahertz (THz) high-harmonic generation (HHG) through dynamical Bloch oscillations in gallium selenide (GaSe). By using THz waveforms with peak fields of 72 MV/cm, the researchers drive coherent interband polarization and dynamical Bloch oscillations in GaSe, resulting in phase-stable HHG across the THz-to-visible spectrum (0.1–675 THz). Quantum interference of different ionization paths is controlled by the THz waveform, and a quantum theory of inter- and intraband dynamics explains the observed phenomena. The results demonstrate all-coherent THz-rate electronics. The THz spectral region, once considered the "THz gap," has become accessible with advanced photonics tools. THz pulses with stable carrier-envelope phase (CEP) and high electric fields enable new optical applications. These pulses can serve as ultrafast bias fields for extreme transport studies, as their photon energies are far below electronic interband resonances in semiconductors. THz biasing, acting on the femtosecond scale, is not limited by dielectric breakdown. The study shows that THz fields can induce intervalley scattering, impact ionization, and ballistic transport in semiconductors. The research demonstrates that Bloch and Zener's prediction of quasi-momentum change in an electric field leads to Bragg reflection and charge oscillations in real and reciprocal space. When the electric field competes with atomic potential gradients, extreme high-field phenomena such as interband ionization, Wannier-Stark localization, and band mixing may occur. While similar phenomena have been studied in artificial structures, coherent high-field transport in bulk solids remains challenging due to ultrafast scattering and small unit cell sizes. The study uses CEP-stable THz waveforms to explore a novel regime of ultrafast coherent charge transport. The THz field drives interband polarization in GaSe, accelerating electron-hole pairs to perform dynamical Bloch oscillations, generating CEP-stable radiation. The HHG spectrum is phase-locked, with CEP-stability confirmed by electro-optic sampling and spectral interferometry. The HHG process is attributed to dynamical Bloch oscillations combined with coherent interband excitation. The study identifies the physical origin of HHG as the interference of multiple excitation pathways, with the CEP of the THz wave controlling the HH spectrum. The results show that CEP-stable THz transients enable record-bandwidth, CEP-stable spectra covering the entire THz-to-visible domain. The study highlights the potential of ultrafast coherent carrier transport for future THz-rate electronics. The findings demonstrate that dynamical Bloch oscillations can probe the electronic band structure of bulk media all-optically, opening new avenues in fundamental solid-state physics.This study explores sub-cycle control of terahertz (THz) high-harmonic generation (HHG) through dynamical Bloch oscillations in gallium selenide (GaSe). By using THz waveforms with peak fields of 72 MV/cm, the researchers drive coherent interband polarization and dynamical Bloch oscillations in GaSe, resulting in phase-stable HHG across the THz-to-visible spectrum (0.1–675 THz). Quantum interference of different ionization paths is controlled by the THz waveform, and a quantum theory of inter- and intraband dynamics explains the observed phenomena. The results demonstrate all-coherent THz-rate electronics. The THz spectral region, once considered the "THz gap," has become accessible with advanced photonics tools. THz pulses with stable carrier-envelope phase (CEP) and high electric fields enable new optical applications. These pulses can serve as ultrafast bias fields for extreme transport studies, as their photon energies are far below electronic interband resonances in semiconductors. THz biasing, acting on the femtosecond scale, is not limited by dielectric breakdown. The study shows that THz fields can induce intervalley scattering, impact ionization, and ballistic transport in semiconductors. The research demonstrates that Bloch and Zener's prediction of quasi-momentum change in an electric field leads to Bragg reflection and charge oscillations in real and reciprocal space. When the electric field competes with atomic potential gradients, extreme high-field phenomena such as interband ionization, Wannier-Stark localization, and band mixing may occur. While similar phenomena have been studied in artificial structures, coherent high-field transport in bulk solids remains challenging due to ultrafast scattering and small unit cell sizes. The study uses CEP-stable THz waveforms to explore a novel regime of ultrafast coherent charge transport. The THz field drives interband polarization in GaSe, accelerating electron-hole pairs to perform dynamical Bloch oscillations, generating CEP-stable radiation. The HHG spectrum is phase-locked, with CEP-stability confirmed by electro-optic sampling and spectral interferometry. The HHG process is attributed to dynamical Bloch oscillations combined with coherent interband excitation. The study identifies the physical origin of HHG as the interference of multiple excitation pathways, with the CEP of the THz wave controlling the HH spectrum. The results show that CEP-stable THz transients enable record-bandwidth, CEP-stable spectra covering the entire THz-to-visible domain. The study highlights the potential of ultrafast coherent carrier transport for future THz-rate electronics. The findings demonstrate that dynamical Bloch oscillations can probe the electronic band structure of bulk media all-optically, opening new avenues in fundamental solid-state physics.