Laser Doppler Velocimetry measurements are performed in flat flames, stabilized on a newly developed flat-flame burner. It is shown that the velocity component perpendicular to the main flow direction, induced by expansion in the reaction zone and buoyancy in the burnt gas, is significant. A method is derived with which the temperature profile of flat flames can be determined from two-dimensional Laser Doppler Velocimetry measurements. Good agreement is found when compared to one-dimensional flame calculations and experimental data obtained from the literature. A method is presented to describe the influence of expansion and buoyancy on the burnt gas flow.