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The operation of high power THz transmitters in the pJ energy range has been recently demonstrated by several groups. However, these transmitters operate at repetition rates of only several Hz. In this paper we report a high power THz transmitter operating at 1 kHz repetition rate. This kHz repetition rate gives a high signal-to-noise ratio, which is essential for quantitative study of high-field semiconductor physics. The transmitter is an undoped GaAs wafer with aluminum electrodes separated by a 3 cm gap. The bias to the antenna is provided by a high voltage pulse generator producing 2 ps pulses with a peak voltage of up to 40 kV. The THz antenna is illuminated at normal incidence by 150 fs, 800 nm pulses from a Clark-MXR Ti:Sapphire regenerative amplifier system running at 1 kHz.The energy of the terahertz pulses was measured with a Molectron pyroelectric detector which is known to have a flat spectral response from the visible up to millimeter wave region. We also used an Infrared Lab liquid helium cooled silicon bolometer for detecting the THz radiation. Our measurement of the highest energy per pulse was 300 nJ, and the energy was found to be a quadratic function of the applied bias voltage. Using a 2.5 inch focal length parabolic mirror, we found that the focal spot has a diameter of approximately 5.5 mm, with an intensity distribution close to Gaussian. Measurements of the pulse energy as a function of laser fluence were also conducted to study the saturation behavior of the antenna. It was found that the 3 cm gap antenna saturates at a laser fluence as low as 35 pJ/cm2, independent of the applied bias. We also observed that a 1 cm gap antenna did not exhibit saturation behavior at a laser fluence above 500 pJ/cm2. Characterization of the THz pulse was done using a Michelson interferometer and a transient mirror. A typical interferogram and the spectrum of the pulse obtained by the interferometer are shown below. 0 8 0 6 -2 0 4 5 $ 0 2 0 0 -0 2 0 4 0 2 4 6 8 I 0 1 2 1 4 l-me gs)