This paper explores the sub-cycle control of terahertz (THz) high-harmonic generation in semiconducting gallium selenide (GaSe) using dynamical Bloch oscillations. The authors use intense, phase-locked THz waveforms with peak fields of 72 MV/cm to drive coherent interband polarization and accelerate electron-hole pairs, generating phase-stable high-harmonic transients across the entire THz-to-visible spectral range (0.1 to 675 THz). The dynamics are controlled by the waveform of the driving field, with quantum interference of different ionization paths explained by a quantum theory of inter- and intraband dynamics. The results demonstrate the first direct verification of coherent control of high-harmonic generation through CEP (carrier-envelope phase) locking, paving the way for all-coherent THz-rate electronics. The study highlights the unique properties of THz pulses, which have extended the scope of optics and enabled resonant control of low-energy excitations and ultrafast transport studies in semiconductors.This paper explores the sub-cycle control of terahertz (THz) high-harmonic generation in semiconducting gallium selenide (GaSe) using dynamical Bloch oscillations. The authors use intense, phase-locked THz waveforms with peak fields of 72 MV/cm to drive coherent interband polarization and accelerate electron-hole pairs, generating phase-stable high-harmonic transients across the entire THz-to-visible spectral range (0.1 to 675 THz). The dynamics are controlled by the waveform of the driving field, with quantum interference of different ionization paths explained by a quantum theory of inter- and intraband dynamics. The results demonstrate the first direct verification of coherent control of high-harmonic generation through CEP (carrier-envelope phase) locking, paving the way for all-coherent THz-rate electronics. The study highlights the unique properties of THz pulses, which have extended the scope of optics and enabled resonant control of low-energy excitations and ultrafast transport studies in semiconductors.