  We investigate the prospects of extending observations of high redshift QSOs
to z>8 by means of a very wide-area near-infrared slitless spectroscopic
survey, e.g. the planned survey with the European Space Agency's Euclid
telescope. For any QSOs at z>8.06 the strong Lyman-alpha line will enter the
wavelength range of the Euclid near-infrared spectrometer and imaging
photometer (NISP). We perform a detailed simulation of Euclid NISP slitless
spectroscopy (with the parameters of the wide survey) in an artificial field
containing QSO spectra at all redshifts up to z=12. The simulation spectra are
analysed with an automated redshift finder, and a detection rate estimated as a
function of H magnitude and redshift. Spectroscopic identification of QSOs
would reach deeper limits for the redshift ranges where either H-alpha
(0.67<z<2.05) or Lyman-alpha (z>8.06) is visible. Furthermore, if
photometrically-selected z>8 spectra can be re-examined and re-fitted to
minimize the effects of spectral contamination, the QSO detection rate in the
Lyman-alpha window will be increased by an estimated 60% and will then be
better here than at any other redshift, with an effective limit H=21.5. With an
extrapolated rate of QSO evolution, we predict the Euclid wide (15000 sq. deg.)
spectroscopic survey will identify 20-35 (19-33 with a small correction for
lineless objects) very luminous QSOs at z>8.06.
