Thomson scattering from plasmas in high‐pressure discharges for rare‐gas halide excimer laser pumping was observed using an yttrium‐aluminum‐garnet laser with a second harmonic generator, combined with a double‐monochromator to reject large signal from Rayleigh scattering. The results showed the electron velocity distribution to be Maxwellian which was different from prediction of computer simulations, while variation of electron density and temperature with time and gas composition was consistent with results of computer simulations.