An asymptotic theory of laminar hypersonic boundary-layer separation f
or large Reynolds number is described for situations when the surface
temperature is small compared with the stagnation temperature of the i
nviscid external gas flow. The interactive boundary-layer structure ne
ar separation is described by well-known triple-deck concepts but, in
contrast to the usual situation, the displacement thickness associated
with the viscous sublayer is too small to influence the external pres
sure distribution (to leading order) for sufficiently small wall tempe
rature. The present interaction takes place between the main part of t
he boundary layer and the external flow and may be described as invisc
id-inviscid. The flow in the viscous sublayer is governed by the class
ical boundary-layer equations and the solution develops a singularity
at the separation point. A main objective of this study is to show how
the singularity may be removed in different circumstances.