The author considers globally defined
$h$
Fourier integral operators
$(h\, {\rm FIO})$
with complex-valued phase functions. Symbolic calculus of
$h\, {\rm FIO}$
is considered and, using a new complex Gauss transform, the composition of
$h$
pseudodifferential operators
$(h\, {\rm PDO})$
and
$h\, {\rm FIO}$
is considered. For a self-adjoint
$h\, {\rm PDO}\, A(h)$
and
$h\, {\rm PDO}\, P(h)$
and
$Q(h)$
with compactly supported symbols, the results are applied to approximate the kernel of the operator
\[
U_{P,Q}(t;h):=P(h)e^{-ih^{-1}tA(h)}Q(h)^{\ast},\quad t\in {\bb R},\;h>0,
\]
by a single, globally defined
$h$
-oscillatory integral.