  This paper presents the results of the characterisation of a thin, fully
depleted pixel sensor manufactured in SOI technology on high-resistivity
substrate with high momentum charged particles. The sensor is thinned to 70
$\mu$m and a thin phosphor layer contact is implanted on the back-plane. Its
response is compared to that of thick sensors of same design in terms of signal
and noise, detection efficiency and single point resolution based on data
collected with 300 GeV pions at the CERN SPS. We observe that the charge
collected and the signal-to-noise ratio scale according to the estimated
thickness of the sensitive volume and the efficiency and single point
resolution of the thinned chip are comparable to those measured for the thick
sensors.
