We have generated femtosecond pulses with a peak power as high as 0.7 GW at the repetition rate of 100 kHz from a downchirped-pulse amplification (DPA) Ti:sapphire laser. For the high-energy amplification with high repetition rate, we employ a regenerative amplifier, acousto-optically switched and pumped by a Q-switched green laser. The DPA-based dispersion control is achieved up to the third-order term by use of a prism-grating stretcher and a glass compressor. We have obtained 28 muJ, 39 fs laser pulses with a compression efficiency of 95 %. Temporal and spatial characteristics of the laser pulses are investigated.