  We present new determinations of effective temperature, surface gravity, and
masses for a sample of 46 hot DA white dwarfs selected from the EUVE and ROSAT
Wide Field Camera bright source lists in the course of a near-IR survey for low
mass companions. Our analysis, based on hydrogen NLTE model atmospheres,
provides a map of LTE correction vectors, which allow a thorough comparison
with previous LTE studies. We find previous studies underestimate both the
systematic errors and the observational scatter in the determination of white
dwarf parameters obtained via fits to model atmospheres.
  The structure of very hot or low mass white dwarfs depends sensitively on
their history. To compute white dwarf masses, we thus use theoretical
mass-radius relations that take into account the complete evolution from the
main sequence. We find a peak mass of our white dwarf sample of 0.59 solar
masses, in agreement with the results of previous analyses. However, we do not
confirm a trend of peak mass with temperature reported in two previous
analyses.
  Analogous to other EUV selected samples, we note a lack of low mass white
dwarfs, and a large fraction of massive white dwarfs. Only one is likely to
have a helium core. While the lack of helium white dwarfs in our sample can be
easily understood from their high cooling rate and therefore low detection
probability in our temperature range, this is not enough to explain the large
fraction of massive white dwarfs. This feature very likely results from a
decreased relative sample volume for low mass white dwarfs caused by
interstellar absorption in EUV selected samples.
