Generation of ultrahigh hydrostatic pressure by application of a strong one-axis deformation is demonstrated in epitaxial films on a mica substrate. This was followed by measurements of transport properties in -type as a function of temperature (100-300 K) and pressure of up to 30 kbar. This pressure allowed studies of the restructuring of the conduction band. The nonmonotonic pressure dependence of the Hall coefficient and the increase of electrical conductivity σ() can only be explained using two subband structures in the conduction band: subbands of light and heavy electrons with a mobility ratio of 10. The gap between the electron subbands increases with the hydrostatic pressure.